[LAD] Let's kill EPAMP???

Stefano D'Angelo zanga.mail at gmail.com
Wed Jun 4 09:46:36 UTC 2008

2008/6/4 Steve Harris <steve at plugin.org.uk>:
> On 3 Jun 2008, at 19:39, Stefano D'Angelo wrote:
>>> #4. Support for time stretching when using non real-time audio sources.
>> I came to this conclusion about it: if combining together pitch
>> shifting and time stretching you can get better results than doing
>> things separately, it is the case to support it at a plugin level;
>> otherwise time stretching can be done by the host and pitch shifting
>> by the plugin.
>> Now, I'm looking at phase vocoders on wikipedia
>> (http://en.wikipedia.org/wiki/Phase_vocoder) and that thing states:
>> "The time scale of the resynthesis does not have to be the same as the
>> time scale of the analysis, allowing for high-quality time-scale
>> modification of the original sound file."
>> I'm no expert in this stuff, does anyone know how if that is true?
> It's true, but it's really, really hard to get right.
> You don't have to use timestretching to resample audio for a music player,
> infact you would avoid that at all costs, you just need to resample.

The question basically was about time-stretching combined with pitch
balancing (output to have the same pitch as the input). Resampling is
a related but different thing; it just happens that you can
time-stretch without balancing the pitch by resampling and not
changing the output sample rate settings.

I guess my English is getting worse lately :-)

>> In such case support should be added and, IMHO, that could be done
>> modifying the run() to return buffer length and give the host an hint
>> on maximum buffer sizes.
>> I think it shouldn't be done inside an extension since it's really
>> core level stuff.
> No, I disagree very strongly. Time stretching is one of a very small number
> of applications for the feature, the user is not going to want to insert it
> into a chain of effects, so just use SRC, and feed the plugins with the
> resampled material.

It's true that it has probably a very small number of applications,
and I understand it can be implemented as an extension, but I don't
think it's right to just claim that "users don't want to do that" and
forget about it.

For example, I'm not sure whether not having that feature prevents or
makes it hard somehow to do stuff like DJ-style scratching or speed
changing effects with sample-level accuracy.

Is it ok for you if I write an extension for it?

> Having plugins being capable of outputting an arbitrary number of samples is
> a really horrible thing to deal with in a realtime environment, I'd want to
> avoid it al all costs.

Well, if you know the maximum output buffer size somehow, I don't see
any reason to be worried about that. Is there something I should know?

> Everything else you said makes sense.

At least :-)


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