[sdiy] 12 bit quantization noise, dithering, synths

[sleepy_dog at gmx.de]

Here, section 2.4, thes mention adding white noise - I hadn't heard of
that before,
what seems more common is a triangular signal, especially at not very
high bit resolutions.
Like in section  "2.5 Improving the Signal-to-noise ratio by adding a
triangular signal"

https://www.ti.com/lit/an/spra461/spra461.pdf


Chris McDowell via Synth-diy:
> Howdy list,
>
> I'm working on some FM synth code running on an STM32G431 (technically PM if you caught discussion a bit ago on this list)
> For the most part, this chip is well suited to "chill" digital synthesis. I've got a handful of voices running 2 operator FM with feedback and loads of envelopes, all pretty satisfying.
> I am using the built-in 12 bit DAC, and finally at the point where the quantization noise on the tails of long envelopes is bothering me. I have a very high-level understanding of what dithering is, and have played a little with naively adding a tiny bit of white noise to my output signal to mask the quantization noise. it DOES work, but the noise floor is really not that low, and I fear I'm misunderstanding some nuance of dithering here and kind of just caveman drowning it out with white noise.
>
> There's no issue besides on the tails of long envelopes. When we get close to silence, there is quite a bit of "hash" and digital goofiness that makes perfect sense given my implementation.
>
> To try to reduce the constant noise floor, I also tried adding the dithering to the envelopes instead of the output. this kind of works, but sounds a bit conspicuous. it's kind of just gating the quantization noise with the envelopes. I think it maybe sounds better than with no attention, but not really "better" than a constant bit of white noise underneath the signal.
>
> One question I have is: does my white noise sample rate need to be higher than my output signal's?
>
> But overall, my question to list is: what are some ways we can go about reducing quantization noise in 12 bit or lower outputs?
>
> Are there some subtle tricks or have I just never noticed 8 or 12 bit systems sounding, yknow, terrible... this could be a classic case of "yeah, listening hyper critically in a quiet room on nice headphones will reveal secrets sometimes", as the noise floor of my QSC PA speakers is actually quite a bit higher than this quantization noise, so I never realized it was there during less attentive testing.
>
> Cheers,
> Chris McDowell
>
>
>
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