Audio interface performance issue

New member here, so please forgive me for my low level understanding of all things Logic, I am working on fixing that. I have posted here because I have quickly run into some performance issues that I would like some advice on.

I have just bought myself Logic 9 having not played around with computer recording for a good few years. I have bought the full version and loaded it onto a pretty new iMac with a 3.06 GHz Core 2 Duo processor and 4GB of RAM. I have no external hard drive, so am using the built in drive to run the software and store audio/midi files.

I am using a brand new Lexicon I-ONIX U22 USB interface (http://www.lexiconpro.com/product.php?id=154 ). I have downloaded and installed up to date drivers.

I am a guitar player, so set about a first project by laying down 4 guitar/bass tracks using Amp Designer (all with Logic pre-set guitar sounds just to get me going) and a single midi drum track (from Apple loops). I didn’t add any plug-ins beyond those that loaded with the pre-set “rigs”.

I found that I ran into problems even on play back. My CPU meter is constantly in the red and playback keeps stopping with a warning that either my hard disk is too slow or I have a performance overload. When I switch to "Built-in" audio rather than the Lexicon, the demand on the CPU is substantially reduced and I don't get the problem.

When I open up the meters there are two narrow meters side by side and labelled together as "Audio". Next to these is a single wider meter labelled "Disc I/O". The overload is on the Audio meter, specifically the right hand of the two side by side meters (not sure what the significance of each individual meter is). Playing back with the built-in audio the right hand Audio meter gets up just past the quarter way point. Playing back with the Lexicon this meter peaks into the red causing the problem.

The only preference I had (knowingly) changed at set up was the buffer - to minimize latency for my guitar playing. I had set it at 64 samples, which I guess is on the low side. If I increase the buffer from 64 samples to 128 samples reduces the problem, and at 256 samples there is no overload problem when using the Lexicon (with the 5 tracks mentioned above), but quoted "round trip latency" increases to 21ms.

However, the built-in audio has no problem with a smaller buffer size. In fact with the built-in audio I can reduce the buffer to 32 samples (with quoted round trip latency of only 3.2ms) without putting any noticeable extra load on the CPU when playing back. Using the built in audio with the buffer set to 256 samples, the "round trip latency" is quoted at 13.3ms (compared with 21ms for the same buffer size using the Lexicon). To get the same quoted latency of 13.3ms using the Lexicon I need to drop the buffer size down to 128 samples.

So, I find two things when comparing the Lexicon with the built-in audio:

1 With the buffer set the same in both cases, the Lexicon loads the CPU much more than the built-in audio, even on playback; and

2 If the buffer is set the same in both cases the quoted "round trip latency" for the Lexicon is higher than for the built-in audio.

I am not sure if these two effects are directly related.

Is this what you would expect? Is it normal for an external interface to load the CPU and add to latency in this way? I guess I was naively expecting the Lexicon to perform “better” than the builit-in audio in all respects.

If this is not what you would expect, then presumably this points to some “problem” with the Lexicon, or its compatibility with Logic.

I did email this question to Lexicon support, but in reply got nothing more than a suggestion I increase buffer size to reduce latency - not really getting to the point of the question.

Hope you can help.

As a general rule you want small buffers for recording (for reduced latency), and large buffers (the larger the better) for mixing/playback, as this will reduce CPU strain.

Af far as roundtrip latencies, I also get less when using built-in (12.7ms at 256)...but my Duet (Firewire) is only behind by 2.3ms (15ms). On the other hand, I also have an EMU 0404 (USB), and that gives 22.8ms roundtrip latency at 256. So it's safe to say it is a matter of the quality the drivers of the external interfaces. Probably the kind of interface (USB vs Firewire) plays a role also.

PS: I think you may find interesting reading point 10 in page 4 of your interface's manual.

Hope that helps.

J.

Thanks jordito, your comments are very helpful. I notice from your signature that you use the Apogee duet. I did consider this before buying the Lexicon but it was nearly twice the price and I don't need the portability. Also, the Lexicon has quite a guitar/desktop friendly design and is a name i recognised from guitar effects processors.

Thanks also for the comment on the manual - and for taking the time to have a look at that. The direct Lexicon's direct monitoring option will be very useful on some occasions, but when relying solely on the Logic Amp sims to generate sound as I have so far to date, the guitar goes in completely dry and so sounds like crap when monitored directly without any processing, so that option is not good for this particular circumstance.

Coincidentally I got home from work today to find I have received a follow up response from Lexicon support today which says:

" I have noticed that the output latency time is much larger than the input latency time. I have requested that a more efficient driver be developed; hopefully the next release will be more efficient."

Clearly they have looked a little deeper into the issue and this is a much more promising response than the first one I received. it seems I was a bit to quick to judge Lexicon support on the basis of the first response alone.

I will wait and see if there are any improved driver updates, as I do like the format of the Lexicon, and I have no issue with the sound quality. But if things don't improve I may turn to the Apogee.

Thanks again for your time.

Matt

Hey Matt, glad to help!

One thing...are you running Snow Leopard? I ask because another forum member was having problems when recording a single audio track on a system similar to yours...the main difference...his interface is an Apogee Duet! Here's the thread:

http://www.logicprohelp.com/viewtopic.php?t=52684&highlight=

I'm running 10.5.8, and last night I did a test by recording my guitar through my EMU 0404 USB interface (whose drivers are pretty bad, at least on windows they're pretty much unusable). I used Amp Designer and also had a drum loop playing while recording directly to my internal drive. I tried different buffer sizes and no errors whatsoever.

So, I'm guessing that your interface is not necessarily the problem.

J.

Well thanks again Jordito - I am indeed running Snow Leopard, and your observation could well save me money - no point switching to a more expensive interface to find the problem has nothing to do with the interface.

Got to hope that if SL is where the problem (or at least part of the problem) lies, Apple will fix it. But I will keep watch for information on this issue. In the meantime, if there is a new driver from Lexicon which improves things I will post again.

Thanks again.

Matt

You could also try, if possible, to do a test with your interface on a computer running Leopard to see if you get the same results and therefore confirm it is a Snow Leopard issue.

Regards,

J.