Re: AudioUnitScheduleParameters with kStereoMixerParam_Volume

[Matt Grippaldi]

I’m not an expert, but I think this method is not as “automagic" as you and I 
both assumed.  I believe what you are really scheduling is sample accurate 
ramping of a parameter change that should be done in a render notification 
callback.  You are responsible for keeping track of the incremental parameter 
values across frames.

So you need to add a render notification callback:
AudioUnitAddRenderNotify(mixerUnit, MixerRenderProc, &mixerUnit/* Or whatever 
you need */);

And the parameter event like this (for example):

AudioUnitParameterEvent parameterEvent = {
    .scope = parameter.mScope,
    .element = parameter.mElement,
    .parameter = parameter.mParameterID,
    .eventType = kParameterEvent_Ramped,
    .eventValues.ramp.startBufferOffset = 0,
    .eventValues.ramp.durationInFrames = 0,
    .eventValues.ramp.startValue = 0.0,
    .eventValues.ramp.endValue = 0.01
};

And this callback that would continually ramp from from a volume of 0.0 to 1.0:

OSStatus MixerRenderProc(void* inRefCon,
                         AudioUnitRenderActionFlags* ioActionFlags,
                         const AudioTimeStamp* inTimeStamp,
                         UInt32 inBusNumber,
                         UInt32 inNumberFrames,
                         AudioBufferList* ioData)
{
    AudioUnit* mixerUnit = (AudioUnit*)inRefCon;
    
    if ((*ioActionFlags & kAudioUnitRenderAction_PreRender) == 
kAudioUnitRenderAction_PreRender)
    {
        parameterEvent.eventValues.ramp.startBufferOffset = 0;
        parameterEvent.eventValues.ramp.durationInFrames = inNumberFrames; 
        CheckError(AudioUnitScheduleParameters(*mixerUnit, &parameterEvent, 1),
                   "ramped volume parameter could not be scheduled");
        if (parameterEvent.eventValues.ramp.endValue >= 1.0)
        {
            parameterEvent.eventValues.ramp.startValue = 0.0;
            parameterEvent.eventValues.ramp.endValue = 0.01;
        }
        else
        {
            parameterEvent.eventValues.ramp.startValue += 0.01;
            parameterEvent.eventValues.ramp.endValue += 0.01;
        }
   }
    return noErr;
}
   
If this is not how this is intended to work I hope someone else answers, 
because I would also like to better understand.
- Matt Grippaldi

> On Jul 22, 2016, at 3:17 AM, Benjamin Federer <benja...@boinx.com> wrote:
> 
> Hello everyone
> 
> I am trying to ramp the input volume for one of the input busses of a stereo 
> mixer unit (part of an AUGraph). Although I don’t get any errors when running 
> my code, nothing happens at all, i.e. no audible volume changes occur. I am 
> unsure what I am missing. Or could it be that the parameter just cannot be 
> ramped at all – although it reports otherwise?
> 
> This is what I got so far:
> 
> 
> AudioUnitParameter parameter = {
>           .mAudioUnit = mixerUnit,
>           .mParameterID = kStereoMixerParam_Volume,
>           .mScope = kAudioUnitScope_Input,
>           .mElement = busNumber
> };
> 
> AudioUnitParameterInfo parameterInfo = {};
> UInt32 parameterInfoSize = sizeof(AudioUnitParameterInfo);
> error = AudioUnitGetProperty(parameter.mAudioUnit, 
> kAudioUnitProperty_ParameterInfo, parameter.mScope, parameter.mParameterID, 
> &parameterInfo, &parameterInfoSize);
> if (error)
> {
>   return error;
> }
> 
> AudioUnitParameterOptions parameterOptions = parameterInfo.flags;
> if ((parameterOptions & kAudioUnitParameterFlag_CanRamp) != 
> kAudioUnitParameterFlag_CanRamp)
> {
>   // parameter cannot be ramped-
>   return paramErr;
> }
> 
> AudioUnitParameterEvent parameterEvent = {
>   .scope = parameter.mScope,
>   .element = parameter.mElement,
>   .parameter = parameter.mParameterID,
>   .eventType = kParameterEvent_Ramped,
>   .eventValues.ramp.startBufferOffset = 0,
>   .eventValues.ramp.durationInFrames = durationInFrames,
>   .eventValues.ramp.startValue = startValue,
>   .eventValues.ramp.endValue = endValue
> };
> 
> error = AudioUnitScheduleParameters(parameter.mAudioUnit, &parameterEvent, 1);
> 
> 
> Thanks for any help in advance
> 
> Benjamin
> _______________________________________________
> Do not post admin requests to the list. They will be ignored.
> Coreaudio-api mailing list      (Coreaudio-api@lists.apple.com)
> Help/Unsubscribe/Update your Subscription:
> https://lists.apple.com/mailman/options/coreaudio-api/mattg%40kinematicsystems.com
> 
> This email sent to ma...@kinematicsystems.com


 _______________________________________________
Do not post admin requests to the list. They will be ignored.
Coreaudio-api mailing list      (Coreaudio-api@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/coreaudio-api/archive%40mail-archive.com

This email sent to arch...@mail-archive.com