Question

Context: iOS5 AUSampler AudioUnit

I’ve been digging around trying to determine is there is a programmatic way to determine the number of presets in a DLS or sf2 file. I was hoping it would be available either through ‘AudioUnitGetProperty’ or ‘AudioUnitGetParameter’ for an AUSampler. Then of course I want to be able to switch presets on the fly. The Docs don’t indicate if this is possible or not.

I’m using the standard code for loading DLS/sf2 per TechNote TN2283. The problem is that with lots of sf2 files it is a trial and error process to find out what the presets are.

-(OSStatus) loadFromDLSOrSoundFont: (NSURL *)bankURL withPatch: (int)presetNumber
    OSStatus result = noErr;
// fill out a bank preset data structure

    AUSamplerBankPresetData bpdata;
    bpdata.bankURL  = (CFURLRef) bankURL;
    bpdata.bankMSB  = kAUSampler_DefaultMelodicBankMSB;
    bpdata.bankLSB  = kAUSampler_DefaultBankLSB;
    bpdata.presetID = (UInt8) presetNumber;

    // set the kAUSamplerProperty_LoadPresetFromBank property

    result = AudioUnitSetProperty(self.mySamplerUnit,
                              kAUSamplerProperty_LoadPresetFromBank,
                              kAudioUnitScope_Global,
                              0,
                              &bpdata,
                              sizeof(bpdata));

    // check for errors
    NSCAssert (result == noErr,
           @"Unable to set the preset property on the Sampler. Error code:%d '%.4s'",
           (int) result,
           (const char *)&result);

    return result;
}

Answer 1

OK – had an answer from an Apple Core Audio engineer:

“There is no API to retrieve the number of presets. The Sampler AU only loads a single instrument at a time from any SF2 or DLS bank, so it does not “digest” the entire bank file (and so has no knowledge of its complete contents).”