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Review/ Korg Pa300 / Operative System 2.0/ Expansion of audio levels

Fundamentals of sound amplitude Just to start getting into the subject, let’s go over some basic concepts about sound physics. Sound is basically produced by tiny changes in the air pressure (oscillation or pulse), produced by an elastic body that has been put under vibration. These changes are transferred via a chain reaction, that reaches our external ear, causing the tympanic membranes to move (together with the internal series of ossicles), which shake within the cochlea (a spiral-shaped cavity filled with liquid and hair cells). The vibrations within the liquid of the inner ear cause the hair cells (cilia) to move, producing an electric impulse (Organ of Corti) which travels to the brain through the auditory nerve and creates the HEARING SENSE.

The two variables that cause this sound phenomenon (and every sound phenomena) are related to the AMPLITUDE and TEMPO of the oscillatory movement.

Some may think that an electronic keyboard such as the Pa300 is an electronic instrument that produces the sound in a digital or electric way. Actually, this is a mistake. What produces the hearing sense is the SPEAKER. This is the actual elastic body that produces the vibrations (it is a membrane that oscillates when stimulated by electric impulses) causing micro changes in the air pressure surrounding us and creating that hearing SENSE.

With the update of the 2.0 OS:

By Ángel Diego Merlo

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The youngest in the family raises his voice, taking the sound feel to an unbelievable enhancement of volume perception. This is thanks to the latest OS version in the Korg Pa300, which adds a mastering compressor expansor at the end of the audio process. KORG listens to the musicians’ needs and implements this mighty feature in the Pa300 models.

Stairway to levels!Rising the audio levels for KORG Pa300!

If we could put a pencil at the top of the speaker and have a piece of paper running in front of it, we would get a picture showing the changes in air pressure throughout a period of time. Actually, there is such a device and it’s called OSCILLOSCOPE. The following is a graph that represents the variations:

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From the graph we can take several important concepts for music in general that we can use to understand SOUND LEVELS in the keyboards:

• NOISE FLOOR: The amplitude of the background noise that every acoustic system has, whether it’s electric or digital. Any signal needs to be away from the floor in order to be heard. The further it is, the better it’s heard.

• DYNAMIC RANGE: The distance between silence and the loudest sound in amplitude that the system can tolerate. From the floor (silence) up to the roof (HEAD ROOM). It is measured in dB1. The wider the range, the better. The human ear has a dynamic range that goes from 0 dB SPL (Sound Pressure Level) to 160 dB SPL, which is the limit the human eardrum can stand.

• SIGNAL-NOISE RELATION: This relation (SIGNAL TO NOISE RATIO) is defined by the difference between the possible dynamic ratio and the noise floor. In any hi-fi sound device, the SNR (Signal to Noise Ratio) should not be under 90 dB of difference.

• PEAKS AND VALLEYS OF SIGNAL: These are the moments of maximum and minimum amplitude that take place within the time of a sound signal. If the amplitude is too strong, it will basically hit against the roof (HEADROOM) causing an AMPLITUDE DISTORTION (sometimes called saturation). If it’s too low, it will not be able to get through the NOISE FLOOR.

1 Decibels are a comparative measure of amplitude, not an absolute value.

TIME

AM

PLIT

UD

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DY

NA

MIC

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AN

GE

NO

ISE

FLO

OR

SIG

NA

L-N

OIS

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ELAT

ION

PEAK OF THE SIGNAL VALLEY OF THE SIGNAL

Now that we have gone over the basic principles of sound, we are ready to understand the challenges that a designer faces when dealing with levels in an electronic instrument. Let’s imagine that we represent the DYNAMIC RANGE of a keyboard, as the capacity of a jug to be filled with water (the ability of the speakers to create a VOLUME FEEL, without causing AMPLITUDE DISTORTION).

First of all, let’s perform a little experiment in our imaginary lab. Let’s imagine that the maximum capacity of our jug is 120 dB. On a table, we put ten glasses that will fill the jug. Each glass has a capacity of 12dB. If we pour the content of each glass inside the jug, it will perfectly contain the total amount of liquid offered by the glasses.

If instead, we have 20 glasses on the table and intend to use them all and they are full of liquid, by the time we pour the eleventh glass in the jug, it will overflow. So in this case, each glass should be filled up to 6 dB each. This way, if we pour the 20 glasses inside the jug, it will not SATURATE with liquid and it will be able to contain them all. The numbers used here are random and simple, just to make the concept clear.

In reality, this is what happens in the Pa300. Some users pointed out that they felt it sound stronger than the Pa50sd. And the feeling seems to be correct. But actually, the big difference between both keyboards is that the Pa50 has a capability of 64 polyphonic voices (64 glasses), while the Pa300 has a capability of 128 polyphonic voices. Regardless if the power of the amplification system is similar in both keyboards (with 3 W of difference). That is the reason why, if we only listen to one instrument and because the polyphonic voices are wide in the Pa300, the levels have to be lower.

Furthermore, when you use the TOTALITY of the polyphonic voices and reach the maximum demand of amplitude (by intensely playing the sounds, with many effects and using the complete sequencer with its 16 multi-timbre parts), then the sound feel will be similar in both keyboards.

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KEY

BO

AR

D A

10 glasses of 12 dB each one. 1 jug of 120 dB.

=

KEY

BO

AR

D B

1 jug of 120 dB.

=20 glasses of 6 dB each one.

The lab challenge

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An example in the real worldLet’s imagine we are in a small room, closely listening to a group of three instruments, all of them at a very high volume:

The hearing feel in that room will be bearable and probably pleasant. The sum of the individual volumes of the instruments will fill our sound expectations, reaching 150 dB SPL, so we will listen clearly and loudly to each instrument.

Let’s imagine, in that same room, the sum of various instruments of the same type and some new ones:

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We will forcedly reach the volume limit our ears can bear. We will exceed the hearing capacity and be close to the limit of pain (what we would call -in terms of electricity- amplitude distortion).

The way to avoid this problem without the instruments stopping is: MOVING AWAY.

That will let us listen to more instruments, clearly now the general volume feel of the group is the same, but the partial volume of each instrument has decreased individually. This is what happens when we add more polyphonic voices or more simultaneous instruments to our synthesizer.

Going deeperThe following presentation is a more technical graphic, which shows how the flow of information influences the process toward reaching the maximum capacity of amplitude in amplification.

Note On MIDI:

Velocity = 127

16 parts of multitimbral

and 128 polyphonic

voices.

MIDI controllers:

CC#07 =127CC#11=12

Insert FX:

Compressor, EQ,

Reverb, Delay...

Common FX(send level):

EQ, Reverb, Aural Exciter...

DSP processing of realtime

signal:

Converssion DAC

Final Amplification:

Electric & acoustical

This is obviously affected by the velocity at which we have sent the NOTE ON commands, the level of amplification in the MIDI CHANNEL, managed by controllers #07 and #11 (volume and expression), the effects that are sent to the inner effects of the PCG (Compressor, Aural Exciter, Delay, etc.), the sum of all these SIGNAL REQUESTS, in all the MIDI channels and all the MULTI-TIMBRE parts (specially the ARRANGER MODE and the SEQUENCER MODE) and the participation of all this AMPLITUDE request in the FINAL effects (as for instance, common reverb, chorus and –now thanks to this new implementation of the OS – Compressor, Limiter, Expander.

The solutions!So, facing this technical situation, how do we increase our FEELING of a HIGHER VOLUME? The options are a few:

• Enhancing the volume feel by amplifying the whole system via an external amplification device, such as a powered speaker or even a whole PA system that could reach levels enough to shake a complete building.

• Changing to a higher quality keyboard where we can have a larger amplification system, such as Pa 600 or Pa900.

• Using a Compressor, limiter, expander, which is one of the NEW FEATURES of the new OS Pa300 v 2.0.

How does a compressor, limiter, expander work?Let’s look at the following amplitude graphic. It’s a digital version of a MIDI file executed by KORG Pa300, without using the FINAL LIMITER (which means, without using the upgrade feature in the OS):

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Due to this being instrumental music, just produced in the keyboard, we can observe that the signal amplitude has peaks and valleys in the volume. There are moments in which there are less instruments in the orchestration -or the playing is softer, and moments in which the volumes rise considerably. The limit of amplitude will be set by the moment in which dynamics are stronger in the sum of all their signals.

A compressor or an expander limiter, is a process of the signal. In the case of our Pa300, it’s a digital process (DSP) that is set before the final amplification phase, so that it helps firstly to COMPRESS THE DYNAMIC DIFFERENCES (attenuating the differences between strong and soft) and secondly to deliver a FEELING OF HIGHER SOUND.

This is not an exclusive technique of our keyboards. Any COMMERCIAL MUSIC is put through this MASTER COMPRESSION process. So what we now have is that FINAL sound much more COMPRESSED, in case we need to use the feature. We will discuss the aesthetics of compression in the future, how to use it, program it and when it is convenient to use. But in order to understand the process, the following graph represents the same music, but now with the Pa300 compressor activated:

The VOLUME feel will be absolutely perceived as increased. There hasn’t been an actual increase because the capacity of our jug is still 120 dB (continuing with the previous example). What happens is that we have softened the differences in volume and this, applied at the length of a musical performance, gives us the FEELING of an enhanced sound. We haven’t exceeded the capacity of the system in amplitude, we have SOFTENED THE DIFFERENCES and then increased the whole result with the EXPANSOR, thus reaching the top edge of the jug.

In this picture that summarizes the new implementation of the 2.0 OS in KORG Pa300, we can understand the upgrade:

Uncompressed signal Compressed-expanded signalPa300 limiter

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In a future review, we will learn how to program and set parameters for the compressors of the PCG (software) and also for the final compressors (master) in our KORG keyboards. There is no doubt that this new feature in the Pa300 will take our professional arranger to a whole new level in the achievement of sound similar to that of a professional master.

We could later discuss aesthetic issues such as if “a master should be very compressed or not” or if we should “use the dynamic range without compression”, but the truth is, the tool is there. It works wonderfully. It DRAMATICALLY ENHANCES THE SOUND FEEL of the Pa300 and all KORG users are grateful for this new UPDATE.

Ángel Diego Merlodiego.merlo@importmusicusa.com

CREDITSContent: Angel Diego MerloTranslation: Denise Francia Illustration: Silvana Noya

Design: Romina Noel Campanelli

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