[sdiy] A new shade of pink (noise)

[Eric Brombaugh]

Yes - the secret sauce of how Stenzel got 128 voices of anti-aliased 
oscillators out of a lowly STM32F373 with the Streichfet was an 
eye-opener. Lots of optimizations that are only obvious *after* someone 
tells you how they work.

I agree 100% on the use of "anti-image" or "reconstruction" for the 
filtering that happens after a DAC - I prefer reconstruction. As I 
became more familiar with the subtleties of discrete-time processing I 
also became more conscious of the difference between imaging and 
aliasing and began to strive to use the terms correctly.

Eric

On 11/24/20 1:14 PM, Richie Burnett wrote:
> Thanks for that link Eric.  Very interesting, I always wondered how they 
> achieved 128 voice poly on the Streichfet.
> 
> The section towards the end about using BLEP techniques to emulate 
> "variable sample rate playback with Zero-Order-Hold" on a modern DSP 
> with fixed sample rate is very interesting.  To me this is the secret to 
> getting that gritty PPG type sound when playing back wavetables at low 
> pitches.  I would call the additional spectral content "Imaging" rather 
> than "Aliasing" though, because it is produced by repeated images of the 
> spectrum due to the sampling process that aren't being supressed 
> properly during playback.  Not aliasing that I think of happened during 
> recording of the wavetable.  A lot of people do seem to call the filter 
> that follows a DAC an "Anti-aliasing filter" though, when it is really 
> an "anti-imaging filter" in my opinion, or even "reconstruction filter" 
> is a better description, I think.
> 
> -Richie,
> 
> 
> 
> 
> -----Original Message----- From: Eric Brombaugh
> Sent: Tuesday, November 24, 2020 6:54 PM
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] A new shade of pink (noise)
> 
> The shortcuts that Stenzel takes in the implementation bear a strong
> resemblance to the band-limited interpolation oscillator bank approach
> that he described in his ADC17 talk a few years ago.
> 
> https://www.youtube.com/watch?v=lpM4Tawq-XU&t=6s
> 
> I think I see a pattern in his thinking...
> 
> Eric
> 
> On 11/24/20 5:57 AM, Tom Wiltshire wrote:
>> There’s an interesting paper by Stefan Stenzel on Github, describing a 
>> new digital pink noise generation algorithm:
>>
>>
>> https://github.com/Stenzel/newshadeofpink/blob/master/newshadeofpink.pdf
>>
>>
>> Has anyone seen this? I’ve read it, but there’s one thing I don’t 
>> understand. In the paper, he talks about taking multiple 1-bit noise 
>> sources (as you would in the Voss0-McCartney algorithm) but instead of 
>> using a “zero order hold” (e.g. “stretching” each sample) to decrease 
>> the sample rate, he uses linear interpolation.
>> This is the bit I don’t get - how do you linearly interpolate a 1-bit 
>> signal? There’s nothing in between!
>> He mentions at one point that the digital signal is to be interpreted 
>> as -1 or +1, which would mean that there is a 0 between the two 
>> values, but I still don’t understand how that makes sense when it’s a 
>> digital signal and not a bit of signal processing maths formula.
>>
>> Any clarifications appreciated. I’d like to understand this method 
>> better, but the paper is very brief, assumes quite a lot of background 
>> I don’t have, and doesn’t provide any worked examples for illustration.
>>
>> Many thanks,
>> Tom
>>
>>
>> ==================
>>         Electric Druid
>> Synth & Stompbox DIY
>> ==================
>>
>>
>>
>>
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