[hatari-devel] Slow sound buffer

[David Savinkoff]

On Jan 18, 2011, Nicolas Pomarède <npomarede at corp.free.fr> wrote: 

Le 18/01/2011 23:20, David Savinkoff a écrit :

> Hi,
>
> Main_WaitOnVbl() waits on each emulated VBL to synchronize the real
> time with the emulated ST. This now has less rounding error but
> probably doesn't make a difference unless it is taken advantage of.
>
> Your question about dma sound raised some issues with:
> #define SAMPLES_PER_FRAME  ((nAudioFrequency+35)/nScreenRefreshRate)
> Furthermore, I changed it (in sound.c) to:
> #define...((nAudioFrequency + d_nAudioFrequency)/nScreenRefreshRate)
> I have to use a different variable to do the frequency offset.
>
> It looks like nAudioFrequency+35 is meant to give more samples per
> frame at lower sample frequencies, but doing this will mess with
> FreqRatio in dmaSnd.c
>
> David

OK, that's what I thought. Also, can you tell more about the /86 and 
/-86 you use ? What is the origin of this value of 86 ?

Nicolas

**************************************************
Hi,

I just tested (more thoroughly) a new patch without frequency
offsetting, and with (nAudioFrequency+35) replaced with
(nAudioFrequency). This improvement is enough for me to
believe (nAudioFrequency+35) 'is' the problem.

(nAudioFrequency/86 + nAudioFrequency) increases the sample rate
by 20/100 of a semitone, or 20 cents, or 1.16%

The synchronization is so good now, that 10 cents would be better;
or maybe we can just 'slip in' or 'swallow' a sample once in a while
to keep the buffer centered. If the buffer gets grossly offset, maybe
it can be reset.

More that could be cleaned in sound.c:
./src/sound.c:#define SAMPLES_PER_FRAME  ((nAudioFrequency+35)/nScreenRefreshRate)
./src/sound.c:          int SamplePerVbl = nAudioFrequency / nScreenRefreshRate;

To:
/src/sound.c:#define SAMPLES_PER_FRAME  (nAudioFrequency/nScreenRefreshRate)
/src/sound.c:          int SamplePerVbl = ...Removed?...

David
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