Re: [LAD] send midi message

From: Pedro Lopez-Cabanillas <pedro.lopez.cabanillas@email-addr-hidden>
Date: Thu Jan 05 2012 - 16:31:32 EET

Hi,

On Thursday 05 January 2012, Dave Stikkolorum wrote:
> Hi all,
>
> I try to write a c program that sends midi notes to the Hydrogen drum
> sequencer.
> I use the alsa library to create a client with an output port.
>
> I attached two files.
>
> loopqueue.c works but loop.c doesn't.
>
> A base drum (note:28) is being send.
>
> I am not succeeding to use direct delivery,
> but it only works with the queue.
>
> Any ideas why?

In both programs you need to connect the output port to some input port (for
instance, a soft synth). To do so, you can insert a call to
snd_seq_connect_to() after creating your port:
        snd_seq_connect_to(seq, port, 20, 0);
Where 20:0 are the client:port numbers of the receiving port.

The problem in loop.c is that you are using the function snd_seq_ev_set_note()
that includes a duration as the 5th parameter. This function will create two
MIDI events in a queue, the first one will be the noteon event, and the second
one will be a noteoff event, scheduled adding the specified duration to the
start time of the former noteon event. That requires a queue for event
scheduling.

If you don't mind about noteoff events, because most percussion synths don't
bother about them anyway, replace that function call by
snd_seq_ev_set_noteon(). There is also a snd_seq_ev_set_noteoff() function as
well.

You may be interested in my C++/Qt4 wrapper around the ALSA sequencer API:
http://drumstick.sourceforge.net/docs/index.html

Here is how a simple program playing a note-on MIDI message using drumstick
looks like:

#include <QApplication>
#include <drumstick.h>

int main(int argc, char **argv) {
    QApplication app(argc, argv, false);

    // create a client object on the heap
    drumstick::MidiClient *client = new drumstick::MidiClient;
    client->open();
    client->setClientName( "MyClient" );

    // create the port
    drumstick::MidiPort *port = client->createPort();
    port->setPortName( "MyPort" );
    port->setCapability( SND_SEQ_PORT_CAP_READ | SND_SEQ_PORT_CAP_SUBS_READ );
    port->setPortType( SND_SEQ_PORT_TYPE_MIDI_GENERIC );
    // subscribe the port to some other client:port
    port->subscribeTo( "20:0" ); // or "name:port", like in "KMidimon:0"

    // create an event object on the stack, to send a note on message
    drumstick::NoteOnEvent ev( 0, 66, 100 );

    ev.setSource( port->getPortId() );
    ev.setSubscribers(); // deliver to all the connected ports
    ev.setDirect(); // not scheduled, deliver immediately
    client->output( &ev ); // or outputDirect() if you prefer not buffered
    client->drainOutput(); // flush the buffer

    // close and clean
    client->close();
    delete client;
    return 0;
}

One program that uses Drumstick to play metronome and drum patterns is
KMetronome: http://kmetronome.sourceforge.net/kmetronome.shtml

Regards,
Pedro
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Received on Thu Jan 5 16:15:02 2012

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