[kill bill]

My GB is doing something crazy!!!!!!!!!!!!!!!! When I record something and edit for a few hours, the tracks stop syncing and the pitch goes crazy even though those parameters hadn't been touched. its really bizarre. this song i was just working on went up like a whole perfect 5th and none of the tracks sync up with eachother. i've tried making mixdowns like that but they sound the same.

another time, I was working on a song and the measures somehow got really off. I had to move a a few of the tracks one measure up and some others one measure back. Overall, the software is behaving really eratically and I haven't a clue as to why.

I've tried restarting, etc etc, everything I know how to do and nothing is working. what in sam hill is my GB doing and how do I fix it?

[analogika]

are you sure you have the latest updates?

[Jacke]

Are you recording using real instruments or via a MIDI keyboard?

[kill bill]

my computer checks for updates weekly and I'm recording real intruments.

[madmacgames]

Recording real instruments (audio), you'll need a decent audio interface to achieve multi-track recording/editing with low latency. The computer's on board audio interface isn't going to cut it; you might get away with a few tracks [but even those will have unacceptable latency to some people], but latency will start cropping up pretty quickly.

Any latency above ~7ms is pretty much unacceptable, and even around that it only works alright if you are going for a "loose" feel or "stage" sound. You'll want less than that to get a real tight sound. Really you want it under 3ms [some would even say that is too much, but on a budget end audio interface that's about the best you can hope for]. 1ms - 1.5ms is ideal.

Also remember that hard disk speed will also affect how many tracks you can play back & record simultaneously (assuming it does not playback from a mixdown buffer in real time, in which case CPU will be more of a factor here than hard disk speed).

And CPU will affect how many you can play back/record with effects in real time.

But if you don't have a decent audio interface, that would be my advise of the first place to start.

[Jacke]

I think that changing the BPM setting on recorded real instruments also has the possibility to fudge things up a bit. (I'm pretty sure remembering having issues with that some time back, though that could have been as far back as in GB1.)

[analogika]

Originally Posted by madmacgames

Recording real instruments (audio), you'll need a decent audio interface to achieve multi-track recording/editing with low latency. The computer's on board audio interface isn't going to cut it; you might get away with a few tracks [but even those will have unacceptable latency to some people], but latency will start cropping up pretty quickly.

This is, in my experience, completely incorrect.

The latency is induced by the DRIVER, not the interface, and only on recording.

All audio material read from disk on playback is pre-buffered and played back with absolutey zero latency, completely regardless of the number of tracks.

Either your hard disk is fast enough to read the audio data, or the whole playback will simply stutter and then stop.

What he's seeing, with weird pitching stuff, has absolutely nothing to do with latency. Might be a problem with material being pitched when he changes the key signature, or when he changes the tempo - or it might be a bug in the software involving either of those engines (pitch or time stretch), which is why I asked about the latest updates.

[madmacgames]

Originally Posted by analogika

This is, in my experience, completely incorrect.

The latency is induced by the DRIVER, not the interface, and only on recording.

Both the driver and the hardware of the interface create the overall latency. Some drivers, such as ASIO are designed to deliver lower latencies than other drivers, but this is really a moot point if the manufacturer gave no consideration to the latency of the hardware [and that whole statement is really moot, since you usually only find ASIO drivers with hardware designed for low latency]. Most consumer audio interfaces, such as the one's built into most computers, were not built with latency in mind. You'll probably pick up at least 20-50ms of latency on a standard consumer interface as a combined result of drivers and hardware.

You also can get increased latency as the number of tracks increases, depending on how the program plays back the existing tracks. There are a number of ways a program can play back multiple tracks, some more hard drive intensive and some more CPU intensive, but I'm not exactly sure what method Garage Band uses.

also I was replying to his concern about tracks not syncing up. He's got more than 1 problem, but tracks not syncing up is a pretty clear indication that you've got too much latency in your system, and if you don't have an interface designed for low latency, then that is the prime suspect on the cause of it.

You're not going to make a 24 track [audio tracks] masterpiece on the built in audio interface. It's just not going to happen.

[madmacgames]

...

[analogika]

Since the channel summing is done by the DAW software, and NOT the driver (unless you're specifically summing through an external digital mixer), it is completely irrelevant whether you're playing back 24 tracks via the internal minijack or an external audio interface. All tracks are pre-buffered and played out through the audio interface at precisely the correct time.

Latency does NOT affect playback.

Latency ONLY affects how quickly a signal that comes in FROM THE OUTSIDE is processed by the machine. So if you're playing an electronic instrument and only hearing the instrument you're playing through the computer's speakers, latency becomes an issue if the drivers aren't fast enough, since you hear what you play with a slight delay.

If you're listening to that source outside of the computer (like any natural instrument - piano, guitar, horn, voice, or if you're running it to your stereo directly through a mixer), latency is ONLY an issue in that it delays the tracks you're recording. Logic, and every other professional DAW, has user-settable latency compensation for this reason, which will automatically shift all recorded tracks by fixed number of samples to compensate for this. (GarageBand, IIRC, does not.)


So how high is the latency on the internal sound card? Apple's CoreAudio was well below 40 samples latency back in the 10.2 days, which translates to less than a millisecond at 44kHz - four years ago. (Note that this is WELL below the latency that nearly all professional digital mixers generate today: Yamaha's PM-5D 64-channel digital console, for example, has 2.5-ms latency at 48kHz.)

What about the direct hardware driver?

Well, just for shits and giggles, I just opened a 27-track Logic file (actually 46 tracks, but maximum simultaneous audio channels - no software instruments - is 27), routed ALL channels to the stereo internal output of my Powerbook speakers, and recorded the full speaker output to another channel using the internal microphone, with latency compensation set to zero in Logic's preferences.

No problem whatsoever. The latency is less than HALF the wave of the kick drum, and that's going out through the speakers and then in through the microphone. Looking at the kick drum signal in an analyser, the peak frequency is around 100 Hz, which makes one waveform 1/100th second, or 10 milliseconds. Half that is 5 milliseconds.

5 milliseconds.

So then I muted all channels except for one and tried it again.

No change in recording latency.

Now, five milliseconds might be noticeable to a highly trained, very finely-tuned player, playing extremely rhythmic music, but it's not going to make any difference to 98% of all music production going on.

And audio latency most certainly has absolutely nothing to with this person's problem. Spending money on a new audio interface is not going to fix it.


Note: A *different* kind of latency happens when you're using an external MIDI keyboard to play GarageBand's internal software instruments. Those are caused by a slow processor. Since all sound is generated in real-time by these instrument plug-ins within the computer, these can be extremely taxing for the CPU (especially with plenty of added effects), and severe delay can and will occur when playing these live via keyboard.
This latency completely disappears once the MIDI track has been recorded (once delays in the recording have been edited out), when playing back, since these audio instruments are pre-buffered along with the recorded audio tracks, mixed, and played out completely simultaneously.