# pcmreadcallback not being called

**URL:** <https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862>\
**Category:** FMOD Engine\
**Created:** [May 8, 2018, 2:22pm UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862 "2018-05-08T14:22:11Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![Oscy](https://avatars.discourse-cdn.com/v4/letter/o/e47774/32.png) [@Oscy](https://qa.fmod.com/u/Oscy)\
**Post date:** [May 8, 2018, 2:22pm UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862/1 "2018-05-08T14:22:11Z")

</div>

I create two sounds, one to record pcm from a microphone and another to send pcm to a speaker. The first sound works fine - I include it’s initialization below just for context. The initialization for both is:

// SOUND 1

```
memset(&exinfo, 0, sizeof(FMOD_CREATESOUNDEXINFO));
exinfo.cbsize = sizeof(FMOD_CREATESOUNDEXINFO);
exinfo.numchannels = recordchannels;
exinfo.format = FMOD_SOUND_FORMAT_PCM16;
exinfo.defaultfrequency = recordrate;
exinfo.length = exinfo.defaultfrequency * sizeof(short) * exinfo.numchannels * 1; 

result = Asystem->createSound(0, FMOD_LOOP_NORMAL | FMOD_OPENUSER, &exinfo, &sound);
ERRCHECK(result);

result = Asystem->recordStart(DEVICE_INDEX, sound, true);
ERRCHECK(result);

result = sound->getLength(&soundlength, FMOD_TIMEUNIT_PCM);
ERRCHECK(result);

```

// SOUND 2  
// Note: I use a different exinfo (exinfo2) for sound2. Is this correct practice?

```
memset(&exinfo2, 0, sizeof(FMOD_CREATESOUNDEXINFO));
exinfo2.cbsize = sizeof(FMOD_CREATESOUNDEXINFO); // Required.
exinfo2.numchannels = 2; // Number of channels in the sound.
exinfo2.defaultfrequency = 1024; // Default playback rate of sound.
exinfo2.decodebuffersize = 1024; // Chunk size of stream update in samples. This will be the amount of data passed to the user callback.
exinfo2.length = exinfo2.defaultfrequency * exinfo2.numchannels * sizeof(signed short) * 1; // Length of PCM data in bytes of whole song (for Sound::getLength)
exinfo2.format = FMOD_SOUND_FORMAT_PCM16; // Data format of sound.
exinfo2.pcmreadcallback = pcmreadcallback; // User callback for reading.

result = Asystem->createSound(0, FMOD_OPENUSER, &exinfo2, &sound2);
ERRCHECK(result);

result = Asystem->playSound(sound2, 0, true, &channel2);
ERRCHECK(result);

channel2->setMode(FMOD_LOOP_NORMAL);
channel2->setPosition(0, FMOD_TIMEUNIT_MS); // this flushes the buffer to ensure the loop mode takes effect

channel2->setPaused(false);

```

I implement the pcmreadcallback function as:

FMOD\_RESULT F\_CALLBACK pcmreadcallback(FMOD\_SOUND\* sound2, void \*data, unsigned int datalen)  
{

```
signed short *stereo16bitbuffer = (signed short *)data;

for (unsigned int sample = 0; sample < datalen / 4; sample++) //16bit stereo (4 bytes per sample)
{

    *stereo16bitbuffer++ = (signed short) speaker_buff[sample] * 32767.0f; // left channel
    *stereo16bitbuffer++ = (signed short) speaker_buff[sample] * 32767.0f; // right channel
}
return FMOD_OK;

```

}

The callback function stops being called at some point. I’d like to send ~1024 (newly generated) values to the speaker every frame. Am I making a mistake in how to do this, and if so, where?

---

<div class="post-metadata">

**Author:** ![cameron-fmod](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/cameron-fmod/32/261_2.png) [@cameron-fmod](https://qa.fmod.com/u/cameron-fmod)\
**Post date:** [May 11, 2018, 6:18am UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862/2 "2018-05-11T06:18:43Z")

</div>

It sounds like you want to record sound from a microphone and play it back while recording. You can actually do this with one sound, and we have an example of this in our LowLevel API examples called ‘record’.

---

<div class="post-metadata">

**Author:** ![Oscy](https://avatars.discourse-cdn.com/v4/letter/o/e47774/32.png) [@Oscy](https://qa.fmod.com/u/Oscy)\
**Post date:** [May 11, 2018, 1:10pm UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862/3 "2018-05-11T13:10:08Z")

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> [@](#):
>
> It sounds like you want to record sound from a microphone and play it back while recording. You can actually do this with one sound, and we have an example of this in our LowLevel API examples called ‘record’.

I need to send PCM samples to the speaker which are independent of those coming from the microphone stream. They’re two different sounds with seperate PCM streams that both need to be handled each frame.  
The pcmreadcallback function seems to be called only once. How can I call it periodically to fill the Sound with new values to send to the speaker?

---

<div class="post-metadata">

**Author:** ![cameron-fmod](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/cameron-fmod/32/261_2.png) [@cameron-fmod](https://qa.fmod.com/u/cameron-fmod)\
**Post date:** [May 16, 2018, 5:04am UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862/4 "2018-05-16T05:04:56Z")

</div>

When creating the sound, using FMOD\_CREATESTREAM will stream the data in chunks as it plays which will need to continuously read the data to play the sand, also using far less memory.

Without that flag,a sound will open as a static sound that is decompressed fully into memory after one read callback.

In our examples project there is a solution called ‘user\_created\_sound’ which shows these two options at work.

---

<div class="post-metadata">

**Author:** ![Oscy](https://avatars.discourse-cdn.com/v4/letter/o/e47774/32.png) [@Oscy](https://qa.fmod.com/u/Oscy)\
**Post date:** [May 17, 2018, 8:50pm UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862/5 "2018-05-17T20:50:14Z")

</div>

> [@](#):
>
> When creating the sound, using FMOD\_CREATESTREAM will stream the data in chunks as it plays which will need to continuously read the data to play the sand, also using far less memory.
> 
> Without that flag,a sound will open as a static sound that is decompressed fully into memory after one read callback.
> 
> In our examples project there is a solution called ‘user\_created\_sound’ which shows these two options at work.

Thanks. I set the mode to FMOD\_CREATESTREAM and now the readcallback function is executing regularly.

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<div class="post-metadata">

**Author:** ![KentJi](https://avatars.discourse-cdn.com/v4/letter/k/58956e/32.png) [@KentJi](https://qa.fmod.com/u/KentJi)\
**Post date:** [April 20, 2019, 1:09pm UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862/6 "2019-04-20T13:09:48Z")

</div>

I try use FMOD\_USERDATA | FMOD\_CREATESTREAM mode to create a sound. This is good in Windows as pcmreadcallback function is called coutinuously. However, pcmreadcallback function only called once when I try use same code in my iphone, How can I solve it?

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<div class="post-metadata">

**Author:** ![brett](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/brett/32/261_2.png) [@brett](https://qa.fmod.com/u/brett)\
**Post date:** [April 22, 2019, 6:29am UTC](https://qa.fmod.com/t/pcmreadcallback-not-being-called/13862/7 "2019-04-22T06:29:06Z")

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I’m guessing you mean FMOD\_OPENUSER not FMOD\_USERDATA (which doesnt exist).  
The callback will call as long as you have a long enough sound for it to be called repeatedly, and you return FMOD\_OK from the callback