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What are the max audio sampling rates+polyphony of old gaming consoles, of retro 8-bit sounds [moved from Scientific Discussion]
WAZAAAAA
post Apr 29 2013, 06:17
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Google didn't help me much on these.

Is there a way to know how much 'sampling rate' expressed in Hz and 'polyphony' did the old gaming consoles such as the NES and Gameboy support on their sound hardwares? This may or may not be a dumb question, as I'm not too much into this stuff, so please bear with me.

I've found on Wikipedia a fine chart showing examples of what kind of devices uses certain sampling rates, but in the list there's not what I'm searching for. Does anyone know?
I've also recently stumbled upon this strange thing called "polyphony" which I didn't fully understand. I have a program that has an option to change the maximum polyphony of it, with numbers that range from 32 to 512. Were 8-bit consoles even capable of playing multiple sounds at once in the first place?

I basically want to know how to make sounds as similar as possible to original retro gaming consoles.
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saratoga
post Apr 30 2013, 21:25
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I don't really see the distinction between a digital function generator clocked off a vco and an analog generator composed of a vco controlled by a digital circuit. Its the same idea described differently.
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benski
post May 1 2013, 16:19
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QUOTE (saratoga @ Apr 30 2013, 15:25) *
I don't really see the distinction between a digital function generator clocked off a vco and an analog generator composed of a vco controlled by a digital circuit. Its the same idea described differently.


Except that the digital function generator necessarily aliases (unless extreme care is taken in the mathematics, which is unlikely).
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stv014
post May 1 2013, 19:03
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QUOTE (benski @ May 1 2013, 17:19) *
Except that the digital function generator necessarily aliases (unless extreme care is taken in the mathematics, which is unlikely).


The generators in early 8-bit machines were often limited to dividing the clock frequency by integer ratios. This avoids aliasing, but the pitch accuracy is not perfect, especially if the clock frequency is low. On the other hand, the SID (C64) allows for high pitch resolution at the expense of aliasing, but the high (~1 MHz) sample rate reduces the level of the aliasing.

This post has been edited by stv014: May 1 2013, 19:04
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benski
post May 1 2013, 19:08
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QUOTE (stv014 @ May 1 2013, 13:03) *
QUOTE (benski @ May 1 2013, 17:19) *
Except that the digital function generator necessarily aliases (unless extreme care is taken in the mathematics, which is unlikely).


The generators in early 8-bit machines were often limited to dividing the clock frequency by integer ratios. This avoids aliasing, but the pitch accuracy is not perfect, especially if the clock frequency is low. On the other hand, the SID (C64) allows for high pitch resolution at the expense of aliasing, but the high (~1 MHz) sample rate reduces the level of the aliasing.


A frequency that is an integer divisor of the sample rate still aliases! Just that the aliased components are harmonically related to the signal so it does not sound as bad.

High sample rates do not change the level of aliasing error in the time-domain. This reason for this is because the discontinuity "width" (e.g. +1 to -1 transition in a square wave) is the same regardless of frequency: the width is theoretically infinitely small (in the analog domain). However, high sample rates cause the aliasing to fall below the hearing threshold within the audible frequency band. Which of course is good enough.

Sorry for being pedantic, I frequently see a lot of misinformation on the internet about digital waveform generation and aliasing, so I figured I would point it out here.

This post has been edited by benski: May 1 2013, 19:26
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stv014
post May 1 2013, 19:50
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QUOTE (benski @ May 1 2013, 20:08) *
A frequency that is an integer divisor of the sample rate still aliases! Just that the aliased components are harmonically related to the signal so it does not sound as bad.


In the case of a simple symmetrical square wave (which is what this type of generator is typically used for, by toggling the output every N samples), the aliasing does not produce components that were not already there in the signal, so the effect is basically just filtering at the highest frequency components. Also, since the sample rate is high (100-250 kHz), it does not really make an audible difference.

Edit: since there is actually no real "DAC" with a reconstruction filter, the above mentioned filtering effect does not apply either.

QUOTE
High sample rates do not change the level of aliasing error in the time-domain.


Which is not of much relevance for audibility (and audible aliasing is what matters in the context of the topic being discussed). The level does become lower in the frequency domain, and as RMS level relative to the signal.

This post has been edited by stv014: May 1 2013, 20:12
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