More questions about latency

[geekgurl]

A recent thread touched on how to fix monitoring latency for a vocalist who was recording, and this got me thinking. I have some other questions, because I am experiencing some serious latency in my new endeavors of recording on PC (I had previously recorded on a stand-alone recorder).

Question 1: What causes monitoring latency? Ie, is processor speed, RAM, and/or software choice et al a possible culprit?

Right now I have a PIII 550 running Windows 98SE with 192MB RAM. It's a general-purpose PC so it has a ton of other programs on it, but I've done my best to limit what runs in the background (ensuring that no extreaneous programs run/appear in the taskbar at startup, turning virus checkers and schedulers off, etc). I have an Echo Gina card I got used and Pro Tools Free, because I already am familiar with Pro Tools a little bit.

I'm basically using this setup to see if I like tracking on a computer; if so, I'll upgrade card and software. But maybe I can't get rid of latency until I get rid of PT Free???

Question 2: If routing monitoring through the mixer, how do you hook it up so that the software/CPU/whatever isn't burdened?

Thank you in advance for your time.

 

[Ethan Winer]

GG,

> What causes monitoring latency? Ie, is processor speed, RAM, and/or software choice et al a possible culprit? <

Playback latency is caused by the DAW sending its audio through a block of memory called a "buffer" on the way to the sound card. When you are playing a mix of four tracks, the DAW program has to read the four Wave files one by one, mix their "numbers" together, and then send the result to the sound card. But there's no way to read four files from the hard drive at exactly the same time. So the DAW program sets aside an area of memory (the buffer) and deposits the mixed "numbers" there. When the buffer is full the DAW tells the sound card, "Hey, here's 1/4 second of audio for you." The DAW then has 1/4 second to read the next chunk from the Wave files and mix them, and deposit that mix in the buffer.

The key element is 1/4 second, and the size of the buffer directly relates to the delay. A project that has only one or two tracks and no extra processing (like EQ or reverb) can use a small buffer, and the DAW will have enough time to do all the math before it has to send the result to the sound card. A more complex project that requires more time to mix and process all the elements needs a larger buffer. And the larger buffer means more delay.

Monitoring latency is exactly the same, except instead of the time required to read a bunch of Wave files, it takes time to apply EQ or other affects. In fact, even doing no processing still requires a buffer to pass the audio through, so there's always some amount of delay from input to output.

> Right now I have a PIII 550 running Windows 98SE with 192MB RAM. <

A friend of mine has a very similar computer with a MOTU 324 interface, and he's able to get the latency down to about 10 milliseconds using Sonar. I've never used PT (free or otherwise) or a Gina card, so I can't comment on that aspect.

> I've done my best to limit what runs in the background <

Yes, this is very important because that directly affects how long it takes the DAW to compute the mix. If it has to share the CPU with other programs running in the background, a larger buffer is needed which results in longer latency delay.

> If routing monitoring through the mixer, how do you hook it up so that the software/CPU/whatever isn't burdened? <

Yes, you want to monitor through the mixer, not the DAW. If you happen to have a Mackie mixer or another brand with direct (insert point) outputs, it's easy. What kind of mixer do you have, and does it have either direct outputs or insert points?

--Ethan

 

[TexRoadkill]

Thats a pretty slow system for more than 8 tracks. You would definately benefit from more RAM. Your HD speed can also affect latency.

Your the only person I've heard of to even get PT Free running on a PC. So chances are ANY software will run better.

 

[Slackmaster2K]

Hang on now, most soundcards today and for a long time have supported zero-latency monitoring (inputs are routed directly to outputs). What kind of soundcard do you have? There should be *NO* latency when you're simultaneously recording and playing back tracks.

Run an output from your soundcard into an input, load up a high hat click track, and hit play/record. The offset between the resulting track and the original track should be about 1ms or less, and it should be totally consistant no matter how many effects or tracks you're running. I've demonstrated this before, but even if you find those old threads I don't think the pictures are still available...maybe I'll redo them.

Latency like this is typically only a problem when you're doing live input processing, which means that you're processing the incoming audio stream and then monitoring the processed signal. As Ethan said, the buffering and processing time is responsible for what you're describing as latency. Even if you don't have any effects on the incoming signal, if you're still monitoring this way you'll still have latency. I'm sorry I don't use PT Free so I can't help there. In n-Track, there's a "Live" button that enables/disables live input processing.

Slackmaster 2000