Optimizing Your UAD's Performance for Logic Pro

December 24, 2008 11:14:11 AM PST

First let me introduce myself. I’m Dan Becker, the Mac Support Guy (MSG??!!). I’m the guy who answers all those macsupport@uaudio.com emails you send in, and hopefully provides solutions (nice to meet all of you!!).

Probably one of the most common email questions I receive in the ol' Mac Support email box regards the use of the UAD products with Logic Pro. So let’s look at how to maximize performance of your UAD products with this popular host application!

Core Audio Settings: "The Buffers"

No. … "The Buffers" is not a UK crossover band. The buffers I’m referring to are Logic Pro’s Process Buffer Range and I/O Buffer Size (Hum along: I/O…I/O…it’s off to work we go!). The first thing to do is open the Logic Pro Core Audio settings window.

Location: Logic Pro / Preferences / Audio / Devices > Core Audio:

Logic Core Audio Preferences

The two Core Audio settings we need to focus on are:

I/O Buffer Size

This parameter determines the size of the buffer used by the audio hardware-for both input and output.

Process Buffer Range

This parameter determines the size of the buffer used to compute mixes and effects. You can choose between Small, Medium, and Large (Small = 512, Medium = 1024, Large = 2048).

The first issue that comes up is that some users will set these buffer values lower to reduce latency when tracking (128 or 256 for example). UAD products are meant to be used in the ‘Mixing and Mastering’ phase of production, due to the latency introduced when using the UAD plug-ins. These lower buffer settings will typically cause pops and clicks, or stuttering in the audio stream. With this in mind, you will want to set the buffers to a minimum of 512 (or even 1024).

The second, and very common, issue is mismatched buffer values. It is very important to have the I/O Buffer Size and the Process Buffer Range match (buffers set to the same value). The UAD products will run on the larger of these two buffer values and if they are mismatched then there can be a decrease in performance as Logic Pro calls the UAD plug-ins more frequently at the smaller of the two buffer sizes.

One last note …

There is a checkbox selection in the Core Audio Preferences pane for "I/O Safety Buffer." When activated, Logic Pro uses an additional buffer to process audio output streams. This is supposed to provide a safeguard against crackling noises, which may occur when using very low I/O buffer size settings. Since you will be setting the I/O Buffer to a larger size (512 and above) we suggest you leave this unchecked (do not select this option).

Plug-in Delay Compensation

Location: Logic Pro / Preferences / Audio / General

Logic Delay Compensation Preferences

Compensation Setting
As noted above, the use of the UAD plug-ins will introduce latency on the track. To compensate for this you must enable the Plug-In Delay Compensation setting in the "General" area of the Audio Preferences. Logic compensates for the latency by calculating the amount of latency caused by plug-ins, and then delaying audio streams by an appropriate amount, or by shifting instrument and audio tracks forward in time. The compensation method depends on the type of channel into which the latency-inducing plug-in is inserted. For best results, set this to "All," which will apply compensation to all channels including the audio, instrument, aux, output, bus, and ReWire channels.

Low Latency Mode
There is a checkbox selection for "Low Latency Mode" immediately below the "Compensation" selections. Many users make the mistake of enabling this function, thinking they will improve latency (make it lower). This is a mistake. When you select this option, Plug-Ins will be bypassed to ensure that the maximum delay that can occur across the entire signal flow (of the current track) remains under the chosen value of the "Limit" selection.

All right … that jolly well wraps up the Logic Settings portion of the Support Report! Time to stand up, take a break, and stretch (and a glass of water ... maybe have a snack … carrot sticks, for example!).

… Are you back now?

Good! Let’s continue.

Odd Issues with Logic Pro: Ghost Audio

An odd issue that sometimes comes up when using UAD products and Logic Pro is "ghost audio" (BOO!). This manifests as a bit of the audio (from the track that is being processed through a plug-in) playing immediately before the actual beginning of the track start point. This only happens to some users, but it can be disconcerting ("what is that sound???"). Essentially, Logic works with the UAD in such a way that the audio may get "stuck" as the data is being called up and may get "output" at an inopportune time. This usually happens when the track comprises a number of small sections (a whole bunch of looped sections pasted together, for example). It typically does not happen on a continuous track (one complete audio track file). It can also happen sometimes if you are doing a bunch of transport commands quickly and then RTZ the playback.

The first solution is to leave a blank space at the beginning of the track (a couple bars of empty space). The other thing you can try is to select the "Release All DSP Resources on AudioUnit Bypass" setting in the UAD Meter / Configuration / HOST COMPATIBILITY section.

This can help to clear the buffer, and may help to avoid the ghost audio issue all together! Please note that the ghost audio problem should be resolved in the upcoming UAD v5.2 release.

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— Dan Becker