Re: A number of simple questions (still a few unanswered)
Re: A number of simple questions (still a few unanswered)
- Subject: Re: A number of simple questions (still a few unanswered)
- From: James McCartney <email@hidden>
- Date: Thu, 07 Feb 2013 10:45:59 -0800
Also useful for expressing durations across a sample rate conversion.
On Feb 6, 2013, at 4:50 PM, Jeff Moore <email@hidden> wrote:
> Fractional sample times are very useful for doing synchronization calculations. They are useful for dealing with durations that are not an integral number of samples, like the wavelength of a 440hz sine wave playing on a 44100 device.
>
> --
>
> Jeff Moore
> Core Audio
> Apple
>
>
>
> On Feb 6, 2013, at 4:44 PM, Seth Willits <email@hidden> wrote:
>
>> On Feb 6, 2013, at 4:12 PM, René J.V. Bertin wrote:
>>
>>>>>> - Why is AudioTimeStamp.mSampleTime a float if it's an integer number of samples?
>>>>
>>>> Still curious why it's a Float64 in the first place. :)
>>>
>>> Who says there's an integer number of samples in a second, and not in say, 3 seconds? And how else would you represent the sample duration for a rate of, say, 17 samples per second?
>>
>>
>> Forgive me since it's already been a few months since I was knee deep in Core Audio, but …
>>
>>
>> That's what mSampleRate is for not, mSampleTime. mSampleTime is the "n" in "the nth sample."
>>
>>
>> For example:
>>
>> memset(&timeStamp, 0, sizeof(timestamp));
>> timestamp.mSampleTime = 0;
>> timestamp.mFlags = kAudioTimeStampSampleTimeValid;
>>
>> for (int sampleIndex = 0; sampleIndex < 44100; sampleIndex += 512) {
>> ...
>> timestamp.mSampleTime = (Float64)sampleIndex;
>> AudioUnitRender(outputUnit, &actionFlags, ×tamp, 0, 512, audioBufferList);
>> ...
>> }
>>
>>
>> AFAICT it's always an integer value.
>>
>>
>> --
>> Seth Willits
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James McCartney
Apple CoreAudio
email@hidden
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