Re: [LAU] Popping sound at the start of every note on Bristol synths.

> Date: Mon, 12 Mar 2012 09:11:46 +1100
> From: lsd@email-addr-hidden
> To: linux-audio-user@email-addr-hidden
> Subject: Re: [LAU] Popping sound at the start of every note on Bristol synths.
>
> On 12/03/12 9:03 AM, Rafael Vega wrote:
> > However, I've found that there is a popping sound at the start of every
> > note. This is more apparent in some models/presets than others. I'm
> > pretty sure my jack configuration is fine (has been working fine with
> > other synths, ardour, puredata, qtractor, etc.) and I've also tried ALSA
> > and two different sound cards (laptop internal and firewire). I also
> > tried outputting Bristol straight to system output, passing through
>
> It may just be that the attack on the amplitude envelope is too fast.
> I'm not sure if Bristol has this problem, but on many synths, with the
> attack time set to its minimum, the envelope opens instantaneously, and
> that can cause a clicking sound. Try increasing the attack time and see
> if that helps.
>
> Thanks

I had a listen through the sample you posted and agree that it is an issue withthe attack time, it was always very aggressive but there was also a recent changefrom a default exponential to default linear attack which probably does not helpwith what you are hearing. You can change back to exponential from the configstage however there is _another_ change that will go into the next release whichis probably the correct fix.
The change is to make the envelope 'time constant'. This is actually not the casewith the current code so if you increase the sampling rate you also increase thefastest attack rate. The fix places the attack at 500us then gives you a rate which is independent of the sampling rate. I can make this a config time option if peopleare interested, it could be a runtime option which I think that is overkill but 500us is still pretty aggressive.
The maximum attack duration does not change, that is also a config option which defaults to 10 seconds however having the parameters being a function of the sampling rate was bad coding.
FYI some background on the changes: I have been doing work on 'low end'systems where I default to half rate sample, 22KHz and 24KHz to reduce the CPUfootprint and hence extend battery life. At the same time I have been working onhigh end systems where we have been reviewing the improved sound quality with96KHz and 192KHz and these really exacerbated the problem. There are other interesting results from the developments. The main filters are Huovilainen's whichare 2x resampling, this was required since the algorithm loses frequency accuracyas it approaches Nyquist. At the higher rates I removed the resampling since the cutofffrequency is now nowhere near Nyquist and the result is that, for the filters at least,the change from 48 to 96KHz is almost free and you can still 'play' the filter at selfoscillation.
Let me review the code differences and perhaps post the new envelope.c on theSourceForge forum. That might not be possible: the envelopes actually drive thesignalling to the engine regarding when to deactivate voices in polyphonic voiceassignments and I don't want any more sticky or lost notes where this signallingmight have changed.
Regards, nick.

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Received on Mon Mar 12 16:15:01 2012