Re: Garbled sound with dssi-vst when using ffado

[Pieter Palmers]

Dominic Sacré wrote:

> Hi,
>
> I'm using a few VST plugins with dssi-vst, all of which produce some
> crackling noise when running JACK using the FFADO backend. They all work
> fine with ALSA, using the same sample rate and buffer sizes (48000/128/3).
>
> At first I thought this noise was somehow produced by the firewire audio
> interface, but in fact I could record it by simply connecting the VST's
> output to Ardour (within JACK).
> A closer look at the recorded waveform revealed what was happening: At a
> regular interval of 3072 frames there were small chunks of audio, each 128
> frames in length, which were simply a copy of the previous 128 frames.
>
> Of course it might well be that this is a bug in dssi-vst, and has nothing
> to do with FFADO. So far I haven't noticed this problem with any other JACK
> client. But I was very surprised that a change of backend could have an
> effect like this on a direct connection between clients.
>
> Any ideas where the problem lies? Is there something I can do to fix this?

I'm forwarding this to the jack devel mailing list, since I don't really
see how ffado can have something to do with this.

Greets,

Pieter
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[cannam]

On Wed, Jul 16, 2008 at 8:47 AM, Pieter Palmers <pieterp@...> wrote:
> Dominic Sacré wrote:
>> I'm using a few VST plugins with dssi-vst, all of which produce some
>> crackling noise when running JACK using the FFADO backend. They all work
>> fine with ALSA, using the same sample rate and buffer sizes (48000/128/3).

When you say they work fine with ALSA, do you mean that they work fine
when using JACK with the ALSA backend instead of the FFADO one?  Or do
you mean that they work fine when using ALSA instead of JACK?


Chris
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[Dominic Sacré]

On Wednesday 16 July 2008 10:08:43 Chris Cannam wrote:

> On Wed, Jul 16, 2008 at 8:47 AM, Pieter Palmers <pieterp@...> wrote:
> > Dominic Sacré wrote:
> >> I'm using a few VST plugins with dssi-vst, all of which produce some
> >> crackling noise when running JACK using the FFADO backend. They all
> >> work fine with ALSA, using the same sample rate and buffer sizes
> >> (48000/128/3).
>
> When you say they work fine with ALSA, do you mean that they work fine
> when using JACK with the ALSA backend instead of the FFADO one?  Or do
> you mean that they work fine when using ALSA instead of JACK?

Sorry, I mean JACK using the ALSA backend.

jackd -R -d alsa -r 48000 -p 128 -n 3
vs.
jackd -R -d firewire -r 48000 -p 128 -n 3

With the former, dssi-vst works fine, with the latter it doesn't. There are
no other differences in the setup I can think of.


Dominic
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[Pieter Palmers]

Dominic Sacré wrote:

> On Wednesday 16 July 2008 10:08:43 Chris Cannam wrote:
>> On Wed, Jul 16, 2008 at 8:47 AM, Pieter Palmers <pieterp@...> wrote:
>>> Dominic Sacré wrote:
>>>> I'm using a few VST plugins with dssi-vst, all of which produce some
>>>> crackling noise when running JACK using the FFADO backend. They all
>>>> work fine with ALSA, using the same sample rate and buffer sizes
>>>> (48000/128/3).
>> When you say they work fine with ALSA, do you mean that they work fine
>> when using JACK with the ALSA backend instead of the FFADO one?  Or do
>> you mean that they work fine when using ALSA instead of JACK?
>
> Sorry, I mean JACK using the ALSA backend.
>
> jackd -R -d alsa -r 48000 -p 128 -n 3
> vs.
> jackd -R -d firewire -r 48000 -p 128 -n 3
>
> With the former, dssi-vst works fine, with the latter it doesn't. There are
> no other differences in the setup I can think of.

What happens if you use larger buffer size settings with the firewire
backend? Although they seem to be identical for alsa and firewire
backends, these parameters do have different side-effects for both.

Greets,

Pieter
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[Dominic Sacré]

On Wednesday 16 July 2008 13:51:42 Pieter Palmers wrote:
> Dominic Sacré wrote:
> > On Wednesday 16 July 2008 10:08:43 Chris Cannam wrote:
> >> On Wed, Jul 16, 2008 at 8:47 AM, Pieter Palmers <pieterp@...>
wrote:

> >>> Dominic Sacré wrote:
> >>>> I'm using a few VST plugins with dssi-vst, all of which produce some
> >>>> crackling noise when running JACK using the FFADO backend. They all
> >>>> work fine with ALSA, using the same sample rate and buffer sizes
> >>>> (48000/128/3).
> >>
> >> When you say they work fine with ALSA, do you mean that they work fine
> >> when using JACK with the ALSA backend instead of the FFADO one?  Or do
> >> you mean that they work fine when using ALSA instead of JACK?
> >
> > Sorry, I mean JACK using the ALSA backend.
> >
> > jackd -R -d alsa -r 48000 -p 128 -n 3
> > vs.
> > jackd -R -d firewire -r 48000 -p 128 -n 3
> >
> > With the former, dssi-vst works fine, with the latter it doesn't. There
> > are no other differences in the setup I can think of.
>
> What happens if you use larger buffer size settings with the firewire
> backend? Although they seem to be identical for alsa and firewire
> backends, these parameters do have different side-effects for both.

With larger buffer sizes things get a little better, but basically the
problem remains. At '-p 256 -n 3' with most sounds the noise only starts
when I play multiple notes at once (all the VSTs I'm using are synths).
At '-p 512 -n 3' the problem is much harder to reproduce, but still there.

Some more observations:

Contrary to what I wrote in my first mail, the number of incorrect samples
is not always 128. With one plugin it's 128 (no matter what period size
JACK is running at), but with another plugin it's much smaller, and
actually varies (roughly between 10 and 30 samples in the audio snippet
I've analyzed).

No matter what JACK's period size is, these errors always occur once every
3072 frames, and the incorrect samples are always the same as those exactly
one JACK period before.

I don't claim to really understand how these things work, but this looks a
lot like the buffers are fed to the next client before the VST plugin is
done writing to it, doesn't it?


Dominic
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[Daniel Wagner-4]

>> A closer look at the recorded waveform revealed what was happening: At a
>> regular interval of 3072 frames there were small chunks of audio, each 128
>> frames in length, which were simply a copy of the previous 128 frames.
>>
>> Of course it might well be that this is a bug in dssi-vst, and has nothing
>> to do with FFADO. So far I haven't noticed this problem with any other JACK
>> client. But I was very surprised that a change of backend could have an
>> effect like this on a direct connection between clients.
>>
>> Any ideas where the problem lies? Is there something I can do to fix this?
>
> I'm forwarding this to the jack devel mailing list, since I don't really
> see how ffado can have something to do with this.

3072 (0xc00) is exaclty the number of ticks per cycle, coincidence?

daniel

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[Dominic Sacré]

On Wednesday 16 July 2008 18:40:15 Dominic Sacré wrote:

> On Wednesday 16 July 2008 13:51:42 Pieter Palmers wrote:
> > Dominic Sacré wrote:
> > > jackd -R -d alsa -r 48000 -p 128 -n 3
> > > vs.
> > > jackd -R -d firewire -r 48000 -p 128 -n 3
> > >
> > > With the former, dssi-vst works fine, with the latter it doesn't.
> > > There are no other differences in the setup I can think of.
> >
> > What happens if you use larger buffer size settings with the firewire
> > backend? Although they seem to be identical for alsa and firewire
> > backends, these parameters do have different side-effects for both.
>
> With larger buffer sizes things get a little better, but basically the
> problem remains. At '-p 256 -n 3' with most sounds the noise only starts
> when I play multiple notes at once (all the VSTs I'm using are synths).
> At '-p 512 -n 3' the problem is much harder to reproduce, but still
> there.
>
> Some more observations:
>
> Contrary to what I wrote in my first mail, the number of incorrect
> samples is not always 128. With one plugin it's 128 (no matter what
> period size JACK is running at), but with another plugin it's much
> smaller, and actually varies (roughly between 10 and 30 samples in the
> audio snippet I've analyzed).
>
> No matter what JACK's period size is, these errors always occur once
> every 3072 frames, and the incorrect samples are always the same as those
> exactly one JACK period before.
>
> I don't claim to really understand how these things work, but this looks
> a lot like the buffers are fed to the next client before the VST plugin
> is done writing to it, doesn't it?

I've found at least one other JACK client that exhibits the same problem:
Phasex. So maybe this isn't a dssi-vst issue after all.
What puzzles me is that with both the VSTs (Crystal, Absynth 4) and Phasex,
the problem usually crops up when I play more than one note at the same
time. On the other hand, I have other apps generating much higher DSP
load, but working fine regardless.

Any clues?


Dominic
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