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, ¶meterEvent, 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 <[email protected]> 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,
> ¶meterInfo, ¶meterInfoSize);
> 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, ¶meterEvent, 1);
>
>
> Thanks for any help in advance
>
> Benjamin
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