Strange playhead timestamps in Logic Pro

Audio Plugins
1

I’m running into a strange issue with Logic Pro and AudioPlayHead’s position info.

When I put the play cursor at the start of the very first bar in the project, my plug-in gets the following positions for the playhead:

getTimeInSamples 540544
getTimeInSamples 540608
getTimeInSamples 540672
getTimeInSamples 540736
getTimeInSamples -383
getTimeInSamples -319
getTimeInSamples -255
getTimeInSamples -191
getTimeInSamples -127
getTimeInSamples -63
getTimeInSamples 0
getTimeInSamples 64
getTimeInSamples 128
getTimeInSamples 192
...

The buffer size is 64. The negative timestamps are not a problem, these are from Logic’s pre-roll feature. However the large numbers at the beginning (540544 etc) make no sense.

To reproduce this, make a new JUCE synth plug-in using Projucer and add the following code to processBlock:

if (auto* thePlayHead = getPlayHead()) {
	if (auto position = thePlayHead->getPosition()) {
		if (position.hasValue() && position->getIsPlaying()) {
			juce::File file = juce::File::getSpecialLocation(juce::File::userDesktopDirectory).getChildFile("debug.txt");
			char buf[100] = { 0 };
			if (position->getTimeInSamples().hasValue()) {
				snprintf(buf, 100, "getTimeInSamples %lld\n", *position->getTimeInSamples());
				file.appendText(buf);
			}
			if (position->getTimeInSeconds().hasValue()) {
				snprintf(buf, 100, "getTimeInSeconds %.10f\n", *position->getTimeInSeconds());
				file.appendText(buf);
			}
			if (position->getPpqPosition().hasValue()) {
				snprintf(buf, 100, "getPpqPosition %.10f\n", *position->getPpqPosition());
				file.appendText(buf);
			}
		}
	}
}
buffer.clear();

This logs the playhead position to a file debug.txt on the desktop.

I’m using JUCE 8.0.8, Logic Pro 11.2.2, Sequoia 15.6.1 on an ARM Mac.

Some notes:

  • It does not go wrong when I use my USB audio interface (a Focusrite Scarlett). It does go wrong with my Mac’s built-in speakers. I tested with sample rate 48000.
  • It seems to depend on the buffer size. With a synth plug-in, any buffer size of 256 and below gives this issue. (Update: actually managed to make it go wrong with 512 and 1024 as well, it just occurs less often.)
  • With an effect plug-in, I need to enable record arming on the track to make it happen (since Logic otherwise uses a buffer size of 1024).
  • You may need to enable looping to make it happen. Or repeat the test a few times (rewind to start of song, press play).
  • It doesn’t just happen on my machine. It has been reproduced by other people too.
  • These strange playhead positions are different every time, seemingly random. The PPQ position is also wrong.

Any thoughts? It seems like a bug in Logic to me. I couldn’t get this to happen with Logic 10.8 but that was also on a different machine, so who knows.

Logic Playback Hitching : Plugin Bug, Logic Issue, Or ID10-T error?
2

The negative timestamps are not a problem, these are from Logic’s pre-roll feature.

Being negative is ok, but they look fishy too, why would it go from -63 to 0 if the buffer size is supposed to be 64?

3

Yeah the negative timestamps seem to be off by 1 sample but I can live with that. :slight_smile:

4

I have nothing constructive to say about the large getTimeInSamples output at the start of your logging except possibly it might represent an uninitialized value until it kicks in for real at -383.

As for why they would go from -63 to 0 if the buffer size is 64: it’s not fishy or off by one, because 0 represents a sample as well, so -63 to 0 is 64 samples.

1 Like
5

Wouldn’t that count sample 0 twice? Once in the -63 to 0 block, and once for 0 - 63? (Which is fine since this is just the playhead position and the playhead can move however it wants, but still.)

6

If that’s what it were doing, then yes. But it’s not, according to the information in your log up there.