[alsa-devel] Range of pitchbend MIDI events

[Clemens Ladisch]

Maurizio Berti wrote:
> I was playing with pyalsa and I realized an unexpected behavior with
> pitchbend events.
> The pitchbend range should be, by MIDI standard, between -8192 and +8191,
> or 0-16384. Being a 3 byte event, it should ignore any subsequent byte
> received.
>
> Using pyalsa I'm able to create events with values greater than 127

The ALSA sequencer does not use the MIDI byte format for its events.

Sequencer events use a 32-bit field for controller values:
http://www.alsa-project.org/alsa-doc/alsa-lib/structsnd__seq__ev__ctrl__t.html
and the entire structure is delivered unchanged to the receiving
sequencer client.

Events get converted into actual MIDI bytes only when they end up at
a real MIDI port.  In that case, only the lowest 14 bits of the value
are put into the two data bytes of the pitchbend event.


Regards,
Clemens