Hi,
>Despite the fact that this function ignores two of its arguments, I just dont
>know how to properly tell it which channels to map to which output buffers.
fluid_synth_process(int len, int nout, float** out) behaves like
fluid_synth_nwrite_float(int len, float** left, float** right). Both functions
are intended
to return synthesized buffers for a number of stereo audio channels
(synth->audio_channels). fluid_synth_process() seems adapted to send audio to
audio card with multiples
stereo audio channels (unlike fluid_synth_write_float(),
fluid_synth_write_s16() which are only useful for only one stereo audio
channel).
The internal mixer stereo audio channels buffers (from 0 to audio_channels-1)
are outputed in the out array in an interleaving format:
(l_audio_chan_0, r_audio_chan_0, l_audio_chan_1, r_audio_chan_1,....).
Consequently nout and out array must be set to sufficient size (nout >= 2 x
synth->audio_channels).
The way a MIDI channel number is mapped to an audio channel number is done
inside the fluidsynth mixer in fluid_rvoice_buffers_mix().
During fluid_rvoice_buffers_mix(), the function is instructed by the voice to
select (mapping) the audio channel buffer number m to mix this voice.
In the actual version the mapping m is function of the MIDI channel of the
voice:
m= 2 x ( MIDI channel number % buf_count) with
with buf_count = max (audio_channels, audio_groups).
Somes pictures are attached to illustrates this.
Hope the author of this API could tell more about the intended unused
parameters int nin, float** in.
jjc
> Message du 26/04/18 14:42
> De : "Tom M."
> A : fluid-dev@nongnu.org
> Copie à :
> Objet : [fluid-dev] API design: fluid_synth_process()
>
> I thought to release a beta in the nearer future. But I would like to have
> the API ready before I do so. One function that still strikes me is
> fluid_synth_process() [1]. It's lacking a real implementation for 15 years.
> If we dont get it right now, we'll never do, so we better discuss it.
>
> This function is used for pulling synthesized audio from the synth. It's said
> to become the "generic interface in future versions". Although its usage is
> discouraged as being still "experimental", it's already established due to
> being required for the callback function of new_fluid_audio_driver2() [2].
>
> Despite the fact that this function ignores two of its arguments, I just dont
> know how to properly tell it which channels to map to which output buffers.
> I'm thinking here in the scope of a "future release" that might support
> surround audio and rendering effects of each midi channel to separate stereo
> / surround buffers.
>
> Does anybody have an idea how to deal with this function (preferably without
> changing its signature)? Any idea of how those two ignored arguments could be
> used? Would welcome any thoughts (esp. from a user perspective).
>
> Tom
>
> [1]:
> http://www.fluidsynth.org/api/synth_8h.html#a1ac90e2732aa652679305f78cbd66670
> [2]:
> http://www.fluidsynth.org/api/audio_8h.html#a3959d8add1dea97e507a5ea2c802c0bc
>
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> fluid-dev mailing list
> fluid-dev@nongnu.org
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>
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