Generating Keymaps

This example automatically generates a custom keymap given a list of audio file paths:

• We import the audio files, detect onsets, and slice them into segments.
• Then analyze each segment’s pitch and loudness, keeping only relevant segments (e.g., pitch, non-silent).
• We quantize pitches to nearest 1/8th tone, export the valid segments as samples, and map them to their pitches.
• We save the final keymap to disk for reuse.

Once the keymap is ready, the script loads a MIDI file and, using an ezsampler, triggers the appropriate audio samples based on the pitch, duration, and velocity of each MIDI event. The final result is rendered as audio.

generating_keymaps.bell

## path to custom keymap file
$keymappath = './custom_keymap.txt';
## initialize keymap as null
$keymap = null;
## check if keymap file exists
if exists($keymappath) == 0 then (
    ## retrieve list of audio media files
    $files = getmediafiles('audio');
    ## initialize sample count
    $count = 1;
    ## iterate over each audio file
    for $file in $files do (
        ## import audio file into a buffer
        $b = importaudio($file);
        ## analyze buffer to detect onsets with specified sensitivity
        $b = $b.analyze(onsets(@alpha 0.2 @silencethreshold 0.05));
        ## extract onset markers
        $markers = $b.getkey('onsets');
        ## compute durations between onsets
        $mdurs = x2dx($markers $b.getkey('duration'));
        ## define analysis operations (pitch estimation and loudness)
        $analysis = pitchmelodia() larm();
        ## iterate over onset markers and corresponding durations
        for $offset in $markers, $dur in $mdurs do (
            ## create buffer segment for each detected onset
            $bufseg = $b.setkey('offset', $offset).setkey('duration', $dur);
            ## analyze buffer segment for pitch and loudness
            $bufseg = $bufseg.analyze($analysis);
            ## retrieve pitch confidence value
            $pitchconf = $bufseg.getkey('pitchmelodia_confidence');
            ## retrieve loudness (larm) value
            $larm = $bufseg.getkey('larm');
            ## filter segments based on pitch confidence and loudness thresholds
            if $pitchconf > 0.25 && $larm > 0.005 then (
                ## retrieve detected pitch
                $pitch = $bufseg.getkey('pitchmelodia');
                ## quantize pitch to nearest eighth-tone step and cast to integer
                $pitch = int(approx($pitch @tonedivision 2));
                ## if pitch not already in keymap, add empty mapping
                if $keymap.$pitch == null then ($keymap _= [$pitch]);
                ## transcribe segment
                $bufseg.transcribe();
                ## render current segment for export
                render(@reset 1 @numchannels 1);
                ## define path for exported sample
                $path = './sample-' + tosymbol($count) + '.wav';
                ## export buffer segment to file
                export($path);
                ## increment sample count
                $count += 1;
                ## map pitch to exported sample path
                $keymap.$pitch _= $path
            ) 
        ) 
    );
    ## write updated keymap to file
    write($keymap, $keymappath) 
) else (
    ## if keymap file exists, read it into memory
    $keymap = read($keymappath) 
);
## import MIDI file containing note events
$events = importmidi('bach.mid');
## iterate over first 64 MIDI events
for $e in $events.left(64) do (
    ## retrieve onset time of MIDI event
    $onset = $e.getkey('onset');
    ## retrieve pitch of MIDI event
    $pitch = $e.getkey('pitch');
    ## retrieve velocity of MIDI event
    $velocity = $e.getkey('velocity');
    ## retrieve duration of MIDI event
    $duration = $e.getkey('duration');
    ## use ezsampler to trigger appropriate sample based on pitch
    ezsampler(
        @pitch $pitch
        @duration $duration
        @velocity $velocity
        @keymap $keymap
    ).transcribe(
        ## place sample at adjusted onset time
        @onset $onset * 0.75
        ## randomize panning position
        @pan rand() 
        ## apply slight gain fadeout
        @gain [0 1 0] [1 0 -0.125] 
    ) 
);
## render full transcription for playback
render(@play 1)