[sdiy] jitter, warmth, and so on

[Richard Wentk]

At 23:52 21/04/2006, Antti Huovilainen wrote:
>On Fri, 21 Apr 2006, John Mahoney wrote:
>
>>         1) Assemble a set of audio files containing sound samples of 
>> various oscillators.
>
>This is in principle a good idea, but it is unlikely that the differences 
>would be audible in solo oscillators (how many really "fat/warm" single 
>oscillator synths do you know?)

I think it would still be revealing though.

Consider this test:

Take a collection of files, and have everyone rate them for fat/warm, 
together with a subjective confidence value. (I.e. 'very obvious' to 
'perceptually borderline')

If there's a consensus, there's a real effect. If the results are random, 
doing any further investigation is likely a waste of time.

>24 vs 16 bits makes no difference here - the dynamic range is non-existant 
>(it's an oscillator afterall) and how many oscillators have noise level 
>below -100 dB?

I've occasionally wondered if 'fat' is related to very low level noise 
introducing a kind of dither. If that's present, it needs 24-bit resolution 
to record it properly.

>>Hz (A in various octaves). WAV files, not MP3, right? (Oh... Should the 
>>audio frequencies be factors of 44100 so the wavelengths are whole 
>>numbers of samples? At least, programmatically generated waves can be such.)
>
>No. This would require all VCOs to be exactly stable with no jitter etc. 
>At which point they would already be equivalent and this test would be 
>pointless.
>This is also absolutely not a requirement for the digital waves. Any 
>halfway decent digital oscillator (which probably counts out CSound and 
>vast majority of modular environments) can be made alias-free at any 
>reasonably low frequency (< 4 khz).

Any recording would have to be at 96kHz using a low-jitter clock.

44.1kHz is barely adequate for high-res audio. (Not a Nyquist issue so much 
as a hardware issue.)

Incidentally, I'm hearing interesting things from people who work with 
digital professionally - such as different DAWs sound very different 
playing the same file at the same resolution. This will influence any test, 
because ideally every recording would have to be created in an identical 
environment.

I found that using a different digital I/O card had an astonishing effect 
on the sound - far, far more than I'd ever have expected.

Richard