Hi Benoit,
Sorry for the late reply.
I originally wrote slidingRMSn for usage in compressors, which is
in essence
what you are doing, so this is certainly an option.
The downsides of using it here are:
1) You have to wait a bit for an estimate of the loudness, so it's
always late.
2) With smaller values of N you get faster reaction, but also more
distortion.
If you can find a way to predict the level of your synth before
you make the
sound, it will sound better, cause you then could avoid these
problems.
If you want to use slidingRMSn, I suggest you look at
https://github.com/magnetophon/faustCompressors
and in particular
https://github.com/magnetophon/faustCompressors/blob/master/RMS_FBFFcompressor_mono.dsp
Note: they where written before slidingReduce was merged upstream
and I haven't
adopted them yet to the new libs, cause I wasn't able to package
the new faust
release for my distro yet.
As to your other questions:
- maxN is a necessary implementation detail: faust needs to know
the maximum
length of a delayline before it can create it.
- N can be the same as maxN if you want. It's just that maxN needs
to be known
at compile-time, and N can vary continuously during use if you
want.
- Choosing N is the hard part. It makes sense to have it related
to your lowest
freq, but the best value you'll have to determine by ear, afaik.
In other synths I've gotten good results by setting the
decay-time of the built-in
limiter per note.
Hope that helps, let me know if you have any other questions!
Cheers,
Bart.
Benoit Delemps <benoitdelemps....@gmail.com> writes:
Hello everyone,
i am trying to build the additive synthesis module like
illustrated in this
example.
https://faust.grame.fr/doc/tutorials/#additive-synthesis
The thing is that the normalization applied at the end of the
signal
(dividing by the number of harmonics) prevents overloading but
in the same
time reduces drastically the level output if the energy in the
spectrum is
low.
So instead of dividing by number of harmonics, i choose to
divide by
ba.slidingRMSn to prevent overloading and maintain the level
ouput.
And here are my questions.
- using slidingRMSn, is this the "good" way to normalize
ouput knowing i
want to maintain the level output even if i drop some
harmonic's energy?
in the documentation, we got:
usage
_ : slidingRMSn(N,maxN) : _
- What is the purpose of maxN ?
- N has to be different of maxN ?
- And last question, how i choose N ?
I tought i should do that:
next_power_of_2(Fs / 2*lowest frequency)
but that doesn't work well at low frequency.
So i did that instead:
next_power_of_2(Fs / lowest frequency)
works fine but don't know really why
here is a sample of my code:
additiveSynth = freq <: par(i,nHarmonics,oscilator(i)):>_<:_,(_
:
ba.slidingRMSn(512,512)) : _/_ :> _*gain : envelope
with{
freq =
vgroup("[0]control",hgroup("params",hslider("fundamental[style:knob]",440,125,3000,0.01)));
gain =
vgroup("[0]control",hgroup("params",hslider("gain[style:knob]",-10,0,-100,0.01):
ba.db2linear(_)));
gate = vgroup("[1]control",button("gate"));
envelope = _*en.asr(0.35,1,0.35,gate);
nHarmonics = 10;
};
I thank you for you help
bests
Benoit
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