a brief overview of the sciences of sound intro to sound part 2 1
TRANSCRIPT
A BRIEF OVERVIEW OF THE SCIENCES OF SOUND
Intro to SoundPart 2
1
Echo and Reverberation
Echo – a discrete reflection of a sound...it is intelligible
Reverberation – a “cloud” of reflections that are indistinguishable (Holman) A little bit of reverb creates a “bloom that subtly
reinforces words and notes” (Cox)...but too much reverb makes sounds unintelligible
“Echo and Reverb” video (1:16)
2
Inverse Square Law3
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.html
The Inverse Square Law4
The Inverse Square Law
Image from Howard & Angus (2009)
5
Boundaries
Image from Howard & Angus (2009)
6
Influences on Sound Propagation(see Holman Ch. 1)
Source radiation patternAbsorptionReflectionDiffractionRefractionConstructive and Destructive Interference
and BeatingDoppler Shift
7
Break
NOTE: Slides that follow are adapted from Rick Pitchford’s COM 353 slides.
8
Waveform Clipping:
Transfer Characteristics of all amplifiers are “S” shaped, curved and flattened at the ends, distorting the output signal if the input is too large. Amplifiers are meant to be used in their linear range to avoid distortion. (When you “go to 11” this may involve distortion!)
Maximum Positive Output
Maximum Negative Output
Gain Compression:
unity gain2:1 gain ratio4:1 gain ratio
knee
threshold
Automatic Gain Control allows the dynamic range of a signal to be reduced. This
can be used to maximize signal intensity while
preventing signal overloads. As the input
signal level passes a set threshold value, a knee is encountered in the transfer characteristic. Beyond the
knee, the gain of the amplifier is lower.
-- GOOD: Speaking BAD: Symphonic orchestra There is also gain expansion NOT the same as BRR compression!
Microphone Frequency Response: (X = frequency, Y = amplitude)
Shotgun, Dyn
Desk, Omni, Dyn
deci
Bel
s -
5dB
per
mar
k
Lav, Omni, Cond
Lav, Omni, Cond
Images from ElectroVoice Corp. documentation
deci
Bel
s -
5dB
per
mar
k
20 100 1K 10K 20K20 100 1K 10K 20K
11
Frequency Equalization:•Frequency equalization is achieved by passing a signal through an amplifier or passive component block with a variable frequency response:
•el-cheapo “tone” control:very limited high-frequency adjustment
•bass and treble controls:low and high frequency level adjustment
•graphic equalizers:placement of slider controls approximates the resultant frequency response
•parametric equalizers:sub-octave resolution and ability to fine-tune the amplitude of each individual frequency band
Frequency
Out
put L
evel
Frequency
Out
put L
evel
Out
put L
evel
Frequency
Frequency
Out
put l
evel
Input Signal
The Goal of EQ:
Change a signal with a sub-standard spectral balance or frequency response by sending it through an amplifier with a variable frequency response.
The output signal has a reshaped, hopefully improved, frequency response.
Frequency
Out
put L
evel
Result
Frequency
Out
put L
evel
EQ Block
•EQ can be used to “flatten” a signal with poor frequency response
•EQ can correct a signal with “path problems” (e.g., long lines = high freq roll-off; recorded on tape)
•EQ can be used for effect (AM radio sound, telephone, etc.) or sweetening (boosting low and/or high frequencies)
•In all cases, don’t over-do it; Less is More
EQ Examples:
sound files from http://www.dougyoungguitar.com/eq_pickuptest.htm
Flat, asrecorded
BassBoosted
MidBoosted
HighsBoosted
Telephone “Good”EQ
end15