M A Y 1 20 6 F I N A L RE P OR T : A U DI O P RO C ES S O R F O R T E L E VI S I O N

IO W A ST ATE UNIV ER S ITY

SE NI OR D ES IGN

CLIENT

Texas Instruments

FACULTY ADVISOR

Dr. Randall Geiger

TEAM MEMBERS

Matthew RenchMorgan HodgeMax JablonskiXuetong MaoBrian Joyce

TABLE OF CONTENTS

Executive Summary...................................................................................................................................................................3

Problem Statement.................................................................................................................................................................... 3

Concept Sketch.............................................................................................................................................................................3

Operating Environment...........................................................................................................................................................4

Intended Use and Intended Users.......................................................................................................................................4

Assumptions................................................................................................................................................................................. 5

Deliverables................................................................................................................................................................................... 5

Approach Used............................................................................................................................................................................. 6

Requirements Statement....................................................................................................................................................6

Functional Requirements...................................................................................................................................................6

Non-Functional Requirements.........................................................................................................................................6

Design Constraints................................................................................................................................................................ 6

Market/Literature................................................................................................................................................................. 7

Technical Approach.............................................................................................................................................................. 8

Testing Approach................................................................................................................................................................12

Resource Requirements........................................................................................................................................................13

Detailed Design......................................................................................................................................................................... 14

Circuit Overview..................................................................................................................................................................14

Voltage Controlled Amplifier.........................................................................................................................................15

Peak Detector........................................................................................................................................................................16

Differential Amplifier........................................................................................................................................................17

Integrator................................................................................................................................................................................17

Project Schedule....................................................................................................................................................................... 18

Work Breakdown................................................................................................................................................................ 20

Expenses................................................................................................................................................................................. 20

Implementation........................................................................................................................................................................ 21

Standards.....................................................................................................................................................................................22

Testing.......................................................................................................................................................................................... 23

Blind Testing......................................................................................................................................................................... 23

Tested Circuit Performance............................................................................................................................................24

Additional Improvements....................................................................................................................................................27

Conclusion...................................................................................................................................................................................27

Appendix...................................................................................................................................................................................... 28

Operating Manual................................................................................................................................................................28

References................................................................................................................................................................................... 30

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EXECUTIVE SUMMARY

With the advent of television, commercials have become an important market, playing a role in the communications field. The purpose of commercials is mostly propagation of products, people, or a particular event. However, in fulfilling the advertiser’s own goals, commercials are also producing various inconveniences to consumers’ daily lives. It can’t be denied that viewers are, to some degree, negatively affected by commercial content.

This audio processor aims to create a friendly and healthy environment for people watching TV programs by leveling the volumes of those commercials which are much higher than TV programs (‘annoying’). Its purpose is to make the audio signal stay in a stable range, to ultimately make transitions between regular TV programming and commercials less noticeable.

PROBLEM STATEMENT

Cable TV channels frequently and intentionally increase the audio level of commercial content to garner attention. This is an annoyance to consumers, and they wish for a solution. While some TVs include audio processing to mitigate this problem, it is believed improvements can be made. The objective of this project is to develop a prototype audio processor with amplitude-leveling capability. According to the requirements, the implementation could be analog, digital, or any combination between.

CONCEPT SKETCH

In a specific use case, the device is connected between the television and the receiver of the speakers using RCA cords. The setup is shown below in Figure 1.

FIGURE 1. USE OF DEVICE CONCEPT SKETCH

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The device targets commercials that have higher average peak amplitudes than the television program, as seen in Figure 2. The device will then adjust the gain of the signals to create more level amplitudes.

OPERATING

ENVIRONMENT

Users that purchase the device will be people who care about the television ‘experience’. They are annoyed by commercials and have actively sought a solution. Therefore, the device is expected to be used with high quality audio speakers and equipment in addition to the standard TV speakers. The device will need to be able to limit the unwanted distortion so it can be used with all ranges of audio equipment from high end to low end.

In order to be used, the device will be paired with a TV at all times. It is expected that it can be used anywhere television streams are watched. This means the device will be indoors or weather protected with access to an AC power source. Thus, running on battery power or weatherproofing will not be addressed. It will be assumed that the humidity is in the range of 20%-60%, and the temperature is in the range of 68-76 °F.

INTENDED USE AND INTENDED USERS

The intended use of the product is to level the volume of ‘annoying’ commercials, those that affect the comfort of the daily consumer. The unit must function together with TV sets and audio systems.

Installation will be the only major part of user interaction of this device. The device will have a set of RCA audio inputs and outputs. The television audio will be connected to the inputs, and the user’s sound system will be connected to the audio output.

The control for the system will consist of an on/off switch on the device as well as two additional parameters that will allow the user to personalize the performance of the device.

During operation, the device will function automatically. One of the goals of the device is to allow the user to become more immersed in the television program without being annoyed by commercials. Therefore, the device will function for the majority of the time without needing any user input.

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FIGURE 2. MODIFICATION OF SIGNAL

ASSUMPTIONS

There will be a 120V AC power outlet available. Television / sound system will have external RCA outputs available to connect the device. Users will have access to the device once installed to change the options. Sound out of the device will be played over speakers that don’t apply a load (unlike headphones)

DELIVERABLES

The final design is an operating prototype of an audio processor with amplitude-leveling capability. It will be an analog circuit that will have practical inputs and outputs allowing for various types of signals to be passed through to speakers.

Once constructed, the prototype is tested against the design document to ensure it meets all of the given constraints and has all the necessary features. The operating prototype is used to perform blind listening tests.

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APPROACH USED

REQUIREMENTS

The audio leveling device is developed for stabilizing the volume of the commercials relative to the television program to allow the customers to enjoy consistent volume levels for all the viewing duration. In other words, the device will make commercials less annoying.

FUNCTIONAL REQUIREMENTS

Input and output audio signals using RCA stereo cables Output audio signal sounds more desirable than input

o Judged by a poll of potential consumers Control the output to be either the processed or original signal Adjust the maximum gain to the modified signal Minimize the distortion in the output signal

o Audio delay is less than 45 mso Frequency distortion is less than 5dB for audible rangeo Noise amplification is less that -30dB of white noise compared to content

Make length/width/height of the device a reasonable range so it can be easily carried inside a room and easily connected to televisions

The operating environment should be between 32o-104oF

NON-FUNCTIONAL REQUIREMENTS

Legal and Regulatory Requirements:Before the device is put into the market, it should have passed relative quality and legality test or certification. However, this audio leveling device, solely being a proof of concept, does not need to meet these requirements.

Physical Requirements:The device should be encased in a durable shell to avoid being affected by the outside environment or accidental damage. It should be portable, and safe for the user to operate.

DESIGN CONSTRAINTS

The device will be active during TV content as well as during commercials. Because of this, the unwanted distortion that the device introduces during a TV program must be minimized.

In order to simplify the design, only the TV audio will be processed by the device. This means that a large processing delay in the system will cause a de-synchronization of the video and audio signal. To mitigate this, the device will delay the audio signal by less than 45 milliseconds. According to Advanced Television Systems Committee, a delay less than 45 milliseconds is unable to be detected by the human ear.i Additionally the device needs to limit frequency distortion. Excessive frequency distortion will cause television programming to sound muffled or tinny. This is distracting and will take away from TV

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content. The device will limit the frequency distortion to less than 5dB. This is less than frequency distortion introduced by a high quality speaker system. ii

Finally, the signal noise will not be amplified. If the signal noise gets amplified, there could be cracking or hissing present in the signal. The device should not amplify white noise to be greater than 30dB. This is the amount of white noise found in un-altered TV programming.

MARKET/LITERATURE

The customer base for a device similar to this project is quite large; almost everyone is annoyed by loud commercials at one point or another. There are a few options already on the market that target a similar customer base. Three competing products were purchased and observed.

The first technology that resembles this problem’s potential solution is Dolby Volume. This is a processor that can be put in a standalone device or integrated inside a television. It debuted in 2008, and has been quite successful, so this shows there is a profit to be made with this sort of technology. The Dolby Volume technology is used in an external device called the GefenTV Auto Volume Stabilizer. The advertisement for this product states, “The GefenTV Auto Volume Stabilizer product is a high-quality volume stabilizer. It actually makes the volume adjustments in such a subtle way that you won't even notice the change.”iii This product uses an analog audio RCA cable.

SRS Labs is another company that has produced a similar but cheaper product. Like Dolby Volume, SRS Labs has the option of integrating the technology into a television as well as an external device. Brands already featuring this technology include: Dish Network, EchoStar, Philips, Samsung, Vizio, Numbericable, and NXP. The technology is advertised to “provide the listener with a comfortable and consistent volume level…The listener chooses the preferred volume level once and can rest assured it will remain constant.”iv SRS Labs offers this technology in two external devices; one with a HDMI cable connection and the other with an analog connection.

The third product found that resembles this project is the Terk VR1 Automatic TV Volume Controller. This is a lower quality and less expensive device than the Dolby Volume and SRS Labs. The Terk is an external device that is connected from the receiver to the television with RCA connectors. It is describe as “a fully automatic device that automatically adjusts loudness to proper listening levels.”v

The CALM (Commercial Advertisement Loudness Mitigation) Act, signed by President Obama on December 15, 2010, requires broadcasters to install technology ensuring commercials air at a volume no louder than the programs in which they appear. However, this does not translate to an elimination of annoying commercials. If a commercial is aired at the maximum loudness of the program in which it appears, this does not mean that the content directly preceding the commercial was at maximum volume. Large amplitude jumps can still occur, proving a continued need for the designed device.

TECHNICAL APPROACH

The approach used for the initial design decisions was very research intensive. Several hours of television programming were recorded for analysis of the methods advertisers use to get people’s attention. In order to develop a method of counteracting the annoyance factor of a commercial signal, knowledge of what objectively makes a commercial irritating is necessary. Low amplitude signals followed by signals with overall higher amplitudes and sharp transitions were two of the main characteristics found that describe annoying signals.

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According to the research, there are generally two ways to process an audio signal to reduce amplitudes: automatic gain controller and dynamic range compression. The automatic gain control will alter the signal similar to Figure 3. The circuit will change the amount of gain to make the amplitude of the signal lower. The dynamic range compression will act as Figure 4. Once the amplitude reaches a certain trigger point, the device will compress the signal and lower the amplitude. An ideal compression would have zero gain after this point; however, it will also introduce a significant amount of distortion.

Both methods have advantages and disadvantages. When applying an automatic gain control, very little distortion is introduced to the signal; however, quieter sounds will also be affected which could result in unheard noises. For example, a whisper may not be heard, but a loud bang would be reduced. Using compression will insure all quiet sounds are heard, but louder noises, such as someone yelling, could be heavily distorted since it is altering the shape of the signal.

For this project, an automatic gain control circuit was chosen; however, it is only activated once a threshold voltage is reached, eliminating the amplification of noise.

1 2 3 4 5 6 7 8 9 10 11 12 130

5

10

15

20

25

30

Automatic Gain Control

OrigianalAltered

Ampl

itude

FIGURE 3. CHARACTERISTICS OF THE AUTOMATIC GAIN CONTROL

1 2 3 4 5 6 7 8 9 10 11 12 130

5

10

15

20

25

30

Compression

OriginalAltered

Ampl

itude

FIGURE 4. CHARACTERISITCS OF DYNAMIC RANGE COMPRESSION

There are also several devices in existence that are very similar to the proposed design. To ensure the best available design is created, three competing products were purchased and run through a series of tests.

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This was a very important step in the research since the results will show pre-existing design possibilities, and allow a comparison for the final prototype device.

To determine which of the competing devices sound the best, several commercial signals were run through them and then jumbled to make the test blind and fair. Group members then listened to the unlabeled signals and rated the signals from best to worst. The results were compiled and can be seen in the pie charts in Figure 5-7. The SRS compressor was the clear winner, which is surprising considering the Gefen is the most expensive and uses the Dolby Volume technology that can also be found in many high-end television sets in the market. The Gefen did fair moderately, being chosen as mid-range in quality a majority of the time. It can clearly be seen that the Terk is not a favorable device, as it often made the audio signals more annoying, and was consistently rated the worst processor.

Gefen

BestMid Worst

FIGURE 5. BLIND TEST RESULTS FOR GEFEN AUDIO PROCESSOR

SRS

BestMid Worst

FIGURE 6. BLIND TEST RESULTS FOR SRS AUDIO PROCESSOR

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Terk

BestMid Worst

FIGURE 7. BLIND TEST RESULTS FOR TERK AUDIO PROCESSOR

From additional test results of the competitive devices, parameters that made the signal sound more desirable were extracted. These parameters were used as the foundation of the circuit design. The gain characteristics of the three devices are shown in Figure 8. From these plots, the knee points at which the device starts altering the signal were observed as well the slope characteristics. In the Gefen (top), amplitudes above .1V were kept at a constant gain, leaving the range of the automatic gain controller to be less than .1V. The SRS (middle) modifies the gain of the signal to potentially always have a constant output level for amplitudes above .2V. Amplitudes less than .2V are unmodified. The Terk (bottom) performs similarly to the SRS but the gain increases for amplitudes less than .1V.

FIGURE 8. GAIN CHARACTERISTICS OF THREE COMPETIVE DEVICES

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The transient responses of the devices were also observed by running a series of pulses through each device. The results are shown in Figure 9 by showing the RMS value of the amplitudes with the original signal shown on top. The Gefen (second) contains a slow settling time, resulting in the “swooping” characteristic. The SRS (third) has a faster settling time but no other unique characteristics. The Terk (bottom) also has a fast settling time, but occasionally will overshoot as seen on the fourth pulse.

TESTING APPROACH

As previously mentioned in the Technical Approach, a survey of devices trying to accomplish feats similar to this project will give comparable results for the final testable device. This is essential in the final evaluation. Additionally, testing devices from other companies gives a reliable template for testing the final prototype. It also gives a solid foundation of data to compare to the end device.

Testing is the most crucial part of this project. Since it is one hundred percent subjective, if people think the signal sounds good, then it is a successful test. A blind test is set up on the project website to allow for a large sample population. A signal processed through our device is compared against the same signal processed through one of the competitive devices or the control signal. With a large enough sample group, enough data is obtained to have a full comparisons of our device.

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FIGURE 9. TRANSIENT RESPONSE OF THREE COMPETIVE DEVICES

FIGURE 10. BLIND TEST LOGIC

To make sure all of the functional requirements are met, the delay of the system, frequency distortion, and noise amplification are measured in the same way used on the competitive devices.

RESOURCE REQUIREMENTS

Access to information regarding commercial audio techniqueso This includes the internet and journal articles on audio manipulation

Information regarding completive deviceso Limited information is publically available through the manufacture’s website, alternative

methods need to be identified such as purchase and reverse engineering of two or three competitors.

Access and ability to record TV streams including audio and videoo Importing audio streams into Matlab or some other audio processing software, such as

Audacity, to evaluate and test different techniques is needed. Audio processing programs (Audacity)

o Once the audio streams have been recorded, they need to be imported into Audacity so the characteristics of the signals may be evaluated. The application of different design aspects should be tested in the software so potential solutions can be evaluated without implementation.

Integrated circuits to implement the designo Analog parts such as op amps, JFETS, resistors, etc. are needed to execute the design in

real-time to perform blind testing and evaluate the effectiveness. A sample of blind test subjects to participate in trials

o A large group of participants is needed to obtain a statistically significant estimate of the effectiveness of the product. A good sample group would represent a wide range of ages, as well as technological backgrounds.

A quiet environment where blind testing can take place without being corrupted by external noises

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DETAILED DESIGN

CIRCUIT OVERVIEW

The TV audio signal is input to a voltage controlled amplifier that is controlled by a feedback loop containing a peak detector and integrator. The peak detector detects the low level of the audio wave as a DC voltage. This voltage is then compared to a desired reference voltage, 1V in this case, and outputs a DC voltage of the difference. The voltage is then integrated which turns the DC voltage into an increasing or decreasing ramp that depends on the sign of the DC voltage from the differential amplifier. This is the signal that controls a JFET in the voltage controlled amplifier that adjusts the overall gain of the system accordingly.

FIGURE 11. CIRCUIT BLOCK DIAGRAM

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VOLTAGE CONTROLLED AMPLIFIER

Both the first and the last steps in the circuit are the voltage controlled amplifier. Because the RCA protocol uses stereo signals, the left and right signal paths must be kept separate but identical. The voltage controlled amplifier has three separate stages.

FIGURE 12. SCHEMATIC OF VOLTAGE CONTROLLED AMPLIFIER

First, there is a 10x attenuation to reduce the input signal from a 2Vpp range signal down to 0.2Vpp. This is necessary because the input voltage is also applied over the drain and source of the JFET. Therefore, a small signal is needed to keep the JFET in the linear region. If the JFET is not in the linear region, distortion is introduced in the signal. This attenuation is done through a resistive network.

The next stage is the variable amplification stage. This stage is a non-inverting amplifier where

V fet=V ¿∗(1+ RlRfet ) where Rl is the user controlled low potentiometer. The value of Rfet is controlled

by the feedback loop to adjust the gain of the amplifier to make the output at the desired level. As the gate voltage of the JFET changes from 0V to -3V, the resistance of the JFET changes from 30Ώ to over 1kΏ. This allows the gain of the amplifier to change from 6 to about 1 as needed. The gate voltage comes in from the feedback loop. This part of the circuit is also where the cutoff is determined. Since the maximum value of Rfet is fixed by the feedback loop, changing Rl will control where the circuit stops increasing the gain. This sets the low cut point for the amplifier. However, if the low cut threshold has not been reached, this amplifier increases the signal amplitude so that it matches the set desired level. Because the left and right signal paths should be the same, the Rl and Rfet are the same for both paths.

After the variable amplification stage, the signal is fed into a simple 10x gain amplifier to get the signal back in the 2Vpp maximum range. This signal is the final output, and it is the input to the feedback loop which begins with the peak detector.

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10kΏ

1kΏ

1kΏ

10kΏ

Input Audio Signal

Input Integrator

Output Audio Signal

Output to Peak Detector

10x Attenuation Variable Amplification 10x Gain

PEAK DETECTOR

The peak detector circuit also has three stages; a summing circuit to convert the left and right ears into a single, a full wave rectifier, and peak detector.

FIGURE 13. SCHEMATIC OF PEAK DETECTOR

Because both the right and left ear signal paths have the same gain, there should only be 1 peak detected between both ears. For this reason, the first step in the peak detector is a weighed summing circuit. This circuit adds the left ear signal and the right ear signal together, and then attenuates by 2. The resulting signal can be used to detect the overall loudness of both channels.

The output of the summer is fed into a precision full wave negative rectifier. This is built from two amplifiers; the first amplifier inverts the positive half of the wave and the second amplifier adds this signal to the already negative part. A full wave rectifier was used instead of a half wave rectifier because a full wave rectifier cuts the potential response time in half. It also marginally improves accuracy since a singular, loud, positive peak would be missed with a half wave rectifier. The rectified wave feeds into the detection system.

The detection circuit is a voltage follower amplifier that is put into a capacitor circuit to store the value. The capacitor has resistances in series that limit how fast it charges and discharges. The capacitor time constant can be computed by multiplying the resistance value by the capacitance value, T=RC. Since R can be controlled by the user, this is where the time response parameter can be controlled. There is also a resistor in parallel with the capacitor which allows the capacitor to discharge. This means the value of the peak detector fades over time. The end result is a representation of the loudness of the audio as it changes over time.

This is compared to the desired loudness in the differential amplifier.

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1kΏ

1kΏ

1kΏ

1kΏ1kΏ

1MΏ

10kΏ

10kΏ

5kΏ

3.3kΏ

1uF

Input from Left EarInput from Right Ear

Output to Differential Amp.

Summer Full Wave Rectifier Peak Detector

DIFFERENTIAL AMPLIFIER

FIGURE 14. SCHEMATIC OF DIFFERENTIAL AMPLIFIER

The differential amplifier is an important part of the circuit. It is used to compare the output of the peak detector circuit to a desired value. Since the peak detector is slowly changing and the reference voltage is DC, the output is a DC voltage equal to the signal level subtracted from the desired voltage level. This output is sent to the integrator.

INTEGRATOR

FIGURE 15. SCHEMATIC OF INTEGRATOR

The integrator circuit is the key to getting the desired output level. First, the integrator receives a DC voltage from the differential amplifier circuit. This voltage will either be positive or negative depending on whether the signal is too loud or too quiet. With this type of input, the integrator’s output will either

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1kΏ1kΏ

1kΏ

1kΏ

Output to integratorInput from peak detector

Desired voltage input

Differential Amplifier

Integrator Biasing Differential Amp.

Input from differential amplifier

680kΏ

10nF

1kΏ1kΏ

1kΏ 1kΏ

-1V Output to voltage controlled amplifier

ramp up or down depending on the sign of the input and with a slope of −1RC

V ¿. Since the peak detector

was used to control the time constants on how fast the circuit responded, the RC time constant here is set to insure the integrator responds faster than the peak detector. This allows the peak detector to be the driving force in circuit response time.

Additionally, if there is a Vin=0, meaning the peak detector output matches the desired level, there will be no change in the output. This signal can be used as the controller for the JFET. The initial conditions on the capacitor are zero, so to put our device in the desired initial circuit gain, a differential amplifier is used to bias the integrator output to -1V.

Overall, the circuit works in the following way:

The audio signal goes small, the peak detector value will go low, making the output of the differential amplifier go high and ramp down the integrator’s voltage. As the differential amplifier’s voltage ramps down, the resistance of the JFET increases which also increases the gain of the variable amplifier. This then increases the amplitude of the output until it matches the desired level. When the amplitude matches the desired level, the output of the differential amplifier goes to zero which makes the integrator hold its current value. This then ultimately makes the gain of the variable amplifier constant. Until the audio input signal changes levels again, the process repeats.

PROJECT SCHEDULE

To keep the team organized and driven, milestones were established in a Gantt chart format. This allowed members to easily see where a given task stood, where it was in terms of date, and to what degree it has been completed. Microsoft Project can be used to gradually change the completion rate of a job, allowing for an easy showcase of where the group itself stands, and if more time needs to be spent on a task to ensure it is completed.

The layout for the schedule of the first and second semester of the project is shown below in Figures 16 and 17. The first semester focused on defining the project by researching characteristics of annoying signals and solutions that would address all of these characteristics. The second semester then focused on designing and implementing a solution to the main offending characteristics because time did not allow all solutions to be addressed.

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FIGURE 16. FIRST SEMESTER GANNTT CHART OF SCHEDULE

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FIGURE 17. SECOND SEMESTER GANNTT CHART OF SCHEDULE

WORK BREAKDOWN

The breakdown of each team member’s contribution for of the project is summarized in Table 1.

TABLE 1. WORK BREAKDOWN SUMMARY

Team Member Documents Competitive

DevicesResearch Programming Website Recordings Presentations Meetings Design Total

Max 12 17 18 2 1 12 7 70 20 159Morgan 17 10 18 2 1 15 7 70 20 160

Matt 18 10 15 2 30 6 7 70 5 163

Brian 17 13 13 21 2 7 5 70 40 188Amy 11 8 18 11 1 5 7 70 20 151Total 75 58 82 38 35 45 33 350 105 821

EXPENSES

The anticipated cost stated in the proposal for this project is $400. A total of $349.56 has been spent on the three competing devices, audio cables, and circuit parts to implement the circuit design. A TV tuner card was also purchased to obtain a large sample of signals.

TABLE 2. TOTAL EXPENSES

Price Breakdown Cost

Competitive Devices

Terk Audiovox $25.54

GefenTV $177.50SRS $47.99

RecordingHauppage TV Tuner $49.99Audio Cables $9.99

ImplementationPotentiometers $11.92Power Supply $10.63RCA Connectors $9.00Project Box $7.00

Total $349.56

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IMPLEMENTATION

The circuit was first implemented on a bread board during the design phase on a test bench. Once the final design was reached, the parts were then soldered on a perforated prototype board. RCA connectors, potentiometers, and power connectors were bought and implemented into the soldered board. A plastic box was then placed over the board to protect it from the environment and keep the users safe.

FIGURE 18. OVERALL SCHEMATIC OF CIRCUIT DESIGN

FIGURE 19. SOLDERED CIRCUIT BOARD

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STANDARDS

In this designed system, the only interference with an already existing system is through RCA cables and into the speaker system. Because of this, the designed system needs to be compatible with both of these standards.

RCA CABLES

CABLE SPECIFICATIONS

Core Configuration 2×75 ohm Coax.Conductor Size 0.126mm² (AWG#27)Ov. Jacket Material Flexible PVC

Ov. Dia.(mm) 2×3.0Ø(0.118")Color Black

ELECTRICAL & MECHANICAL CHARACTERISTICS

DC Resistance at 20°CInner Cond. 0.15ohm/m (0.046ohm/Ft)Shield 0.04ohm/m (0.012ohm/Ft)

Capacitance at 1kHz, 20°C 59pF/m(16.8pF/Ft)Characteristic Impedance at 10MHz 75 ohm±5%Attenuation (10MHz) 0.007neper/m (0.0021neper/Ft)Phase Constant (10MHz) 0.28rad/mElectromagnetic Noise* 0.1mV Max.Voltage Breakdown Must Withstand at DC 500V/15sec.Insulation Resistance 1000000Mohm × m Min. at DC 500V, 20°CFlex Life* 24,000 cyclesTensile Strength 40kgEmigration Non-Emigrant to ABS resinApplicable Temperature -20°C~+60°C (-4°F~+140°F)Standard UL Subject 758 AWM 2552 VW-1 60°C 30V, -F-Maximum temp. rating 60C (140F). Maximum voltage 30V Suitable for Class 2 wiring of electrical equipment. *Attenuation: 1 dB=0.1151 neper (1 neper=8.686 dB)*Using standard testing methods.

SPEAKERS

The input level of the speakers varies between different brands. The output range of the designed device should be between –1V and 1V. This will be ensured by latching the output to stay in the range. However, this feature will be implemented in future revisions. Once this feature is implemented, the designed device will be compatible with all speaker input levels.

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TESTING

As stated in the Testing Approach, the device performance was tested by conducting a blind test as well as calculating the delay, distortion introduced, noise amplification, and gain and transient characteristics.

BLIND TESTING

From an online poll set up on the project’s website, statistical information was collected determining if the output signal sounded more pleasant than the original and the other competitive devices. Fellow senior design students as well as family and friends were asked to participant in the survey by answering the questions shown in Figure 20 on the website. Each participant was given a different grouping of signals by randomizing the signal played against the designed device.

FIGURE 20. SCREENSHOT OF ONLINE POLL

The participants then listened to the two signals in each poll and pick which signal sounds more annoying. The data was recorded and summarized in Table 3. The total number of times the signal was

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picked to be more annoying is shown in the 2nd column. In all cases, the designed device was chosen to be the better sounding signal more times than the opponent.

TABLE 3. BLIND TEST RESULTS

Designed Device vs Original Total Original 8 Designed Device 1

Designed Device vs Terk Audiovox Terk Audiovox 11 Designed Device 8

Designed Device vs Gefen Gefen 13 Designed Device 11

Desgined Device vs SRS SRS 17 Designed Device 5

Approximately 25 participants took part in the online poll and each listened to 3 sets of signals. By using a confidence interval analysis, it can be concluded with a 99% confidence interval that the designed device will be picked 59% to 73% of the time for being the better sounding signal.

TESTED CIRCUIT PERFORMANCE

To determine if the device is working as expected and meets the requirements, various characteristics were observed through similar tests that were used on the competitive devices.

To determine the steady state gain characteristics, varying voltage level signals were applied to the input, and the output voltage level was recorded. Figure 21 displays Vin plotted against the gain, Vout/Vin. For already quiet signals, the gain is unchanged. In this way, any static or back-ground noise is not amplified into the circuit. Once the TV audio input exceeds a threshold loudness, the gain is decreased to keep the output amplitude constant.

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FIGURE 21. STEADY STATE GAIN CHARACTERISTICS OF DESIGNED DEVICE

The transient response was also measured by looking at a signal with rapidly-changing amplitudes, shown in Figure 22. Different sweeps of white noise were run through the device, simulating how the circuit will respond to real-world broadcast signals. From this, the settling time was measured by changing the amplitude of the input signal and measuring the time it took for the output to settle at the corresponding level. This value was measured to be 40ms.

FIGURE 22. TRANSIENT RESPONSE OF DESIGNED DEVICE

The distortion the device introduces into the signal was measured by running a signal of white noise through the device and observing the response. The analysis of the response was done by taking the Fourier transform of the output signal and observing the frequency versus amplitude in dB relationship. As seen in Figure 23, very little is distortion is introduced until around 20kHz which happens to be the high end limit of the hearing range to humans. For frequencies in the audible range of less than 20kHz, the device meets the function requirement of having less than 5dB of frequency distortion.

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FIGURE 23. DISTORTION INTRODUCED FROM DEVICE

To determine if the device satisfies the function requirement of having less than -30db of noise amplification, a signal made of 5 different frequencies was ran through the device and analyzed with a Fourier transform. From Figure 24, it can be seen that for the entire signal, the noise amplification is always less than -30db.

FIGURE 24. TEST TO MEASURE NOISE AMPLIFICATION

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The delay of the system was measured by observing the output response of a changing input with an oscilloscope. Figure 25 shows the screen shot of this measurement, and the delay is calculated by observing how long it takes the output to reach the same level as the input. The delay was found to be .4ms which is well within the function requirement of being less than 45ms.

FIGURE 25. OSCILLISCOPE SCREENSHOT OF MEASUREMENT OF DELAY

ADDITIONAL IMPROVEMENTS

The next step for the project would be to optimize the circuit design by using the least amount of components as possible. Additional features could also be added including a wireless remote control, user controls such as silencing the audio for a certain amount of time if a button is pressed, or integrating the circuit inside of the television. The circuit can be improved by implementing a clamping circuit at the output to ensure the voltage is never more than 2Vpp to protect speaker systems that may be attached.

In continuation of this project, the same functionality could be attempted using digital signal processing instead of an analog circuit, or attempt to detect commercial transitions to allow a more aggressive algorithm to be applied without affecting the TV programing.

CONCLUSION

The objective of this project was to design a prototype audio processor with amplitude leveling capability that will make commercials less annoying. The first half of the project focused on researching annoying characteristics to turn a subjective proposal into an objective problem. Once annoying signals were defined, more research was done on solutions for each of these characteristics. The second half of the project focused on only one of these solutions since time restricted design of all solutions. An analog circuit was designed and implemented to perform automatic gain control on a signal to output a constant level amplitude signal. A blind test was performed that statistically proved the signal ran through the designed circuit sounds more pleasant than the original, as well as the competing products already on the market.

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APPENDIX

OPERATING MANUAL

PANEL LAYOUT

1. Bypass Switch2. Low Cut Control3. Time Response4. Analog L/R (RCA) Inputs5. Analog L/R (RCA) Outputs

CONNECT INTO TV STYSTEM

Insert RCA cables from the audio source into the Audio Input jacks on the device (3).

Use the second set of RCA cables to connect the Audio Output (4) jacks to the receiver/audio system input.

Make sure the light next the Bypass switch is off, otherwise press the Bypass switch.

CONNECT POWER SUPPLY TO WALL

Connect the provided 20V power adapter to the power receptacle.

USER CONTROLS

Bypass: If the user wishes to turn off the device, push the bypass switch to output an unaltered signal.

Low Cut: If the user wishes to set the low level where the device will begin to modify the amplitude of the signal, adjust this knob. This control allows the user to make small adjustments to eliminate noise.

Time Response: This knob will modify the circuit’s reaction time to changes in the input amplitude. If annoying transitions are audible, the response can be adjusted to the user’s liking.

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FIGURE 26. DEVICE LAYOUT

Bypass Switch

Low Cut Contro

Time Response

Analog Input

Analog Output

1. 2. 4.

REFERENCES

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i "ATSC Implementation Subcommittee Finding: Relative Timing of Sound and Vision for Broadcast Operations Advanced Television." ATSC Implementation Subcommittee Finding: Relative Timing of Sound and Vision for Broadcast Operations (2003). Advanced Television Systems Committee. Web. <http://www.atsc.org/cms/standards/is_191.pdf>.

ii “MR5mk2: Owner’s Manual,” http://www.mackie.com/products/mrmk2series/pdf/mr5mk2_om.pdf.

iii "GefenTV Auto Volume Stabilizer." Gefen, LLC. Web. 31 Oct. 2011. <http://www.gefen.com/kvm/dproduct.jsp?prod_id=8707>.

iv "TruVolume." SRS Labs: Solutions. Web. 31 Oct. 2011. <http://www.srslabs.com/content.aspx?id=1953>

v "Terk VR1 Automatic TV Volume Controller." Amazon.com: Online Shopping for Electronics, Apparel, Computers, Books, DVDs & More. Web. 31 Oct. 2011. <http://www.amazon.com/Terk-VR1-Automatic-TV-ontroller/dp/B00008VWOJ/ref=sr_1_1?s=electronics>.V “Technical Specs of Component Video Cable.”<http://www.svideo.com/mogami3spec.html>