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Re: iPhone Custom Audio Unit: why buzz?

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Re: iPhone Custom Audio Unit: why buzz?

Subject: Re: iPhone Custom Audio Unit: why buzz?
From: Sung <email@hidden>
Date: Sat, 6 Mar 2010 06:23:20 -0800

Thanks for the reply.

Making 'j' static didn't make a difference. In AudioQueue, I can definitely hear 'clicks' if

I don't keep track of starting frame count of each callbacks. AU seems different, strange.

I checked inNumberFrames = 512. Either way, it didn't help.

You're also right about being safe with 32767. No change though.

static OSStatus renderInput(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags,

const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData)

{

double frequency = 440.0;

static double j = 0.0;

double cycleLength = kGraphSampleRate / frequency;

SInt16 *toneBuffer = (SInt16 *)ioData->mBuffers[0].mData

for (UInt32 frame; frame<inNumberFrames; ++frame)

{

Float32 nextFloat = sin(j/cycleLength * (M_PI*2.0)) ;

toneBuffer[frame] = 32767.0*nextFloat;

j += 1.0;

if (j>cycleLength) {

j = j - cycleLength;

}

return noErr;

}

On Sat, Mar 6, 2010 at 2:03 AM, tahome izwah <email@hidden> wrote:

Of course it buzzes if your cycle length doesn't coincide with
inNumberFrames. You need to remember your "j" across calls (make it
static to see if it solves your problem).

Also, why are you using 512 instead of inNumberFrames in your loop?
That doesn't make much sense to me as there is no reason to believe
that inNumberFrames will always be 512 frames.

In addition, your sine wave will cause digital clipping (wrapping)
when you multiply the result of the sin() call by 32768. Make sure you
limit your output to the range -32768...32767 to be on the safe side.

HTH
--th

2010/3/6 Sung <email@hidden>:

> Hi all,
> There was a thread about creating a custom AU to play a simple sine wave:
> http://lists.apple.com/archives/coreaudio-api/2008/nov/msg00292.html
> I did the same thing and use the DefaultOutputUnit example from Apple sample
> to construct sine tone in callback:
> static OSStatus renderInput(void *inRefCon, AudioUnitRenderActionFlags
> *ioActionFlags,
> const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32
> inNumberFrames, AudioBufferList *ioData)
> {
>    double frequency = 440.0;
> double j = 0.0;
> double cycleLength = kGraphSampleRate / frequency;
>    SInt16 *toneBuffer = (SInt16 *)ioData->mBuffers[0].mData
> for (UInt32 frame; frame<512; ++frame)
> {
> Float32 nextFloat = sin(j/cycleLength * (M_PI*2.0)) ;
> toneBuffer[frame] = 32768.0*nextFloat;
> j += 1.0;
> if (j>cycleLength) {
> j = j - cycleLength;
> }
> }
>    return noErr;
> }
> It works in iphone simulator, but :
> - the sound that comes out is "buzz saw" noise instead of a pure sine tone.
> - on a device, the sound only comes out of headphone, not through the
> speaker.
> Does any of you have similar issues?
>
>

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Follow-Ups:
- Re: iPhone Custom Audio Unit: why buzz?
  - From: Hamilton Feltman <email@hidden>
- Re: iPhone Custom Audio Unit: why buzz?
  - From: tahome izwah <email@hidden>

References:
	>iPhone Custom Audio Unit: why buzz? (From: Sung <email@hidden>)
	>Re: iPhone Custom Audio Unit: why buzz? (From: tahome izwah <email@hidden>)

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