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Using UAD Powered Plug-Ins with Pro Tools, Part 2
2010-01-20


UAD in Pro Tools - Part 2


In the first part of this article, I discussed my initial experiences while running UAD powered plug-ins in Pro Tools, installing and using the UAD2-Quad card in my HD rig. As I stated earlier, I could not be happier with my UAD2 and my mixes have never sounded better. However, when running 3rd party DSP powered plug-ins in Pro Tools, there are some additional concerns that must be addressed to successfully welcome these outsiders into the fold. In part two of our discussion of all things UAD, I will cover some of the Pro Tools specific quirks that UAD users need to account for during recording and mixing, including delay compensation using Mellowmuse's ATA plug-in and using UA's LiveTrack mode.

Understanding and addressing latency concerns:


Like any hardware powered DSP system, the UAD powered plug-ins will incur a small delay with each instance. This additional delay is beyond the normal system latency you experience during recording, set by the playback engine's hardware buffer setting, found under Setup > Playback Engine. This processing delay is inevitable, as the round trip from the disk to the UAD card's DSP is a necessary evil of powered processing. It is worth noting that this delay is not exclusive to the UAD system, or even hardware powered plug-ins. Such delay is also very common in many native RTAS processors, especially "look-ahead" style plug-ins such as brick-wall limiters and tuning plug-ins, so learning how to handle these plug-ins is a vital skill for any Pro Tools user.


Before we seek a solution to this dubious plug-in delay, it is important to understand the problems it creates. Unlike the latency you experience during real-time recording, plug-in induced latency varies track by track, and is directly related to the type and number of processors inserted on each track of your session. Because some plug-in processors (like the UAD powered plug-ins) induce a small amount of delay when inserted, while other plug-ins do not, this causes certain tracks in the session to lag behind the rest, often causing phase and timing issues in the mix. When mixing with a powered plug-in system like the UAD, it is vital that you understand and compensate for these delays.

Knowing is half the battle


Prior to compensating for any plug-in delay, it is nice to know if you have any in the first place. Fortunately, there is a really easy way to check for plug-in or mixer induced delay on Pro Tools tracks. From the mix window, simply Command-click (or Control-click on PC) directly on a tracks Vol/Peak/Delay display (located beneath its volume fader, right under the track type icon) until it reads “dly” (for example, you will need to command-click twice if “Vol” is displayed). This value is displayed in samples, you can convert samples to milliseconds simply by taking your sample delay, dividing it by your sample rate and multiplying it by 1000. So if your delay was 128 samples at a sample rate of 44.1Khz, that would be 128/44100 x 1000 = 2.9ms. Basically, if delay reads “0,” then you have nothing to worry about. If the delay shows a number like “128”, then you have a few options to consider.

QUAD


In the latest version of the UAD software (5.4.1), most UAD powered plug-ins will incur a delay of one buffer size per instance (assuming the plug-in is not in "LiveTrack" mode, more on that later). In other words, if your hardware buffer setting is set to 512 samples (located under: Setup > Playback Engine), and you were running a UAD 1176LN with a Cambridge EQ, the cumulative delay would be 1024 samples (about 23ms at a sample rate of 44.1Khz), or 512 samples per plug-in. Some UAD powered plug-ins need to do internal up-sampling to maintain emulation accuracy during processing, these incur slightly more delay. For example, the Neve 1073 incurs 543 samples of delay at a H/W buffer setting of 512 samples. At any rate, even at the lowest buffer settings, a few UAD powered plug-ins per track will incur enough delay to cause trouble if not compensated for. UA recommends that you set the H/W buffer to either 512 or 1024 samples, but on my rig I was able to run it at 128 samples on lighter sessions. While lowering the buffer size doesn't increase the load on the UAD's DSP, it does increase the load on your CPU, so newer multi-core machines should do better in this regard.



If you are using a DAW other than Pro Tools, you probably don't have to do anything special when mixing with UAD powered plug-ins, as chances are your rig supports plug-in delay compensation or "PDC." A long-time complaint amongst users of Pro Tools LE and M-Powered, automatic PDC has yet to make it into the native versions of Pro Tools and some wonder if it ever will (Pro Tools HD users have enjoyed delay compensation for over 5 years now). Now I'm not here to throw stones, I just want to show you how to deal with the problem if you are working in Pro Tools LE or M-Powered (if you are using Pro Tools HD, I've got you covered a bit further down). As it turns out, things aren't nearly as bad as they used to be. The pain that once robbed precious creative time, manually calculating and adjusting for plug-in induced delay, has been somewhat relieved with the addition of Mellowmuse's ingenious ATA plug-in, which now ships free with every UAD2 system.



Using ATA in Pro Tools LE/M-Powered


The basic idea of any PDC system is that all tracks in the session incur the same amount of delay, thus eliminating any timing or phasing issues associated with some tracks lagging behind others. How most systems (including Pro Tools HD) accomplish this is to calculate the delay of the track with the most latency and work backwards from there. Let's call this longest delay "X" samples. Tracks without any latency (a track without plug-ins for example) will get delayed by X samples, while tracks with a delay less than X will be delayed by X - Y, where "Y" is the amount of delay on the track in question. When all tracks, including auxiliary returns, exhibit the same amount of latency, we have a happy mixer. Like I said, because Pro Tools LE/M-Powered doesn't do this for us automatically, we can use the ATA plug-in to calculate and compensate for us.

While the instructional videos on
Mellowmuse.com are super helpful when setting this up, here is a quick
breakdown of how the ATA plug-in is used in Pro Tools:


QUAD


1. First insert ATA as the first plug-in on every track of your session, including the Master Fader and any Aux Tracks.

2. Inside the ATA plug-in window, set the plug-in's "group" selector to the type of track it is located on (Audio for audio tracks, Aux 1 for Auxiliary Returns, and Master for the Master Fader)

3. Submix all audio tracks into a new stereo aux track, again placing the ATA plug-in as the first insert on this new aux. This is necessary to compensate for delay incurred on the effects returns.

4. Make sure nothing is muted, soloed or set to -infinity, and click the "P" or Ping button on the Master Fader to calculate and compensate for delay.

5. If you are going to do second or third order sends (Using sends on your aux tracks) you will need to use "Aux 2,3,4,5" groups to compensate for additional latency (e.g. feeding a delay into a reverb, or using a send on a submix). The video at mellowmuse.com really helps to understand this.

6. Be sure to ping the master fader each time you insert a new plug-in, as that additional plug-in may change the delay on that specific track.

Note: You will not see the "Dly" indicator change to reflect all tracks having the same latency. The delay is compensated for internally inside the ATA plug-in.
The cool thing about ATA is that it actually polls the delay using an audio "ping," which provides a super accurate measure of delay (some plug-ins report their delay to the host incorrectly). I recommend setting up session templates that have the ATA plug-ins, submix and effects return routing already set up. If you follow the instructions, it works flawlessly and is way better than having to manually compensate for delay, but I'm not gonna lie, this is sort of a cumbersome workaround if you use a lot of second and third order sends in your mixes (seriously, set up templates). But if you are going to point fingers, it's really not Universal Audio or Mellowmuse's fault. Avid needs to come up with a PDC solution for its LE/M-powered users and join the 21st century like every other DAW has.

UAD LiveTrack mode


The UAD2 system now supports a super cool mode called LiveTrack that allows you to use the UAD plug-ins in near real time (e.g. during recording) without the usual "one buffer period" latency that I referred to earlier. You can enable LiveTrack mode by clicking on the little microphone icon on the bottom left of a UAD plug-in window. While LiveTrack doesn't take up anymore resources as far as the UAD card is concerned, it does put a significant strain on your processor compared to normal use, but I found I was able to use it quite extensively during production without taxing my first generation Quad-Core MacPro too much. This LiveTrack mode could definitely pave the way for more "performance" oriented plug-ins on the UAD platform like guitar amp simulators and virtual instruments.

Compensating for the UAD in Pro Tools HD


HD system’s using TDM plug-ins and TDM mixer always suffer from small amounts of routing delay due to the inherent nature of hardware DSP processing and the UAD powered plug-ins aren't too different in terms of why latency occurs. While the complexities of the TDM processing infrastructure are way beyond this article, one should note that plug-in latency is a serious concern when using plug-ins in Pro Tools HD, so serious that Digidesign added a comprehensive delay compensation engine in version 6.4 of the Pro Tools HD software. While I personally try to forget about the days before automatic delay compensation in Pro Tools HD, I am consistently surprised at the number of HD users that fail to take advantage of such a critical tool in the mixing process, a tool that makes using the UAD a dream when compared to more manual solutions like ATA.

Enabling Delay Compensation:


QUAD


Because almost all routing tasks in the HD mixer cause at least a few samples of delay, automatic delay compensation is really a mixers best friend and a near hands-off approach for dealing with plug-in latency. To activate delay compensation, you must first enable it for your system in the Playback Engine (Setup > Playback Engine). The “Delay Compensation Engine” can be set to either Short (for up to 1024 samples of compensation) or Long (up to 4095 samples of compensation). If a session is currently open, Pro Tools will automatically save, close and reopen the session to enable the delay compensation engine. Once enabled in the Playback Engine, you can turn delay compensation on and off by selecting Operations > Delay Compensation.

Short or Long?


The delay compensation engine should be set according to the type of plug-ins you plan on using versus the amount of DSP resources you want to dedicate to delay compensation. Certain plug-ins cause more than 1024 samples of delay (many real-time “tuning” plug-ins, pitch shifters, etc) and therefore would not be sufficiently compensated for under the “short” setting. I found that when using the UAD2 system, Long delay compensation was the best way to go, that way I didn't have to stress out about keeping my H/W buffer size low. The down side of using longer delay compensation settings is that it cuts into the amount of available DSP your system has for other TDM plug-in processing/routing. Remember, lowering the H/W buffer size will keep your UAD plug-ins from causing more delay than the mixer can handle, this is especially important if you are using second/third order sends (sends on aux tracks) in your mixes.

Viewing delay compensation


The Pro Tools HD mixer has a special view just for delay compensation, access this by choosing View > Mix Window > Delay Compensation. Here you will find the tracks total delay (as accumulated by either plug-ins or bus routing), a manual offset control, and the tracks total compensation. “dly” and “cmp” are calculated and adjusted automatically, so for the most part you can watch it do its magic and mix away, knowing you are taken care of. These values are displayed in samples by default, but can be switched to millisecond in the preferences > operation tab.

QUAD


The longest delay in the session is denoted in orange and if a track’s total delay exceeds the engines maximum compensation amount (1024 for short and 4095 for long), it will glow red. When a track’s delay exceeds the total amount of delay compensation available you should always disable that track’s compensation by Control+Command-Clicking (Mac) or Start+Control-Clicking (PC) on the word “dly” in the delay compensation view. This will disable the delay detection on the track and at that point the track can be compensated for manually. I almost always disable the delay on my master fader as the delay incurred there already effects the entire session and need not be compensated for.

Tips for using delay compensation with the UAD system


* Remember, the delay that UAD powered plug-ins cause is directly related to the H/W buffer setting in your playback engine.

* Use LiveTrack mode to reduce delay on aux tracks and second order send returns to avoid using up all your available compensation. This requires you to be extra vigilant as LiveTrack mode will reset when you re-open the session. I noticed that sometimes I had to disable and re-enable delay compensation to get it to show the correct delay after entering LiveTrack mode, this was usually the case in larger sessions.

* Disable delay compensation for your final output's master fader, it will help you conserve available compensation and since all tracks hit this master fader anyways, delay isn't a concern.

UAD Headroom management for HD users


While not related to delay, mixer headroom is of great concern to UAD users mixing in Pro Tools HD. In a previous Pro Tools corner I discussed the fact that inserts on a TDM (HD) system have 24-bit inputs and outputs, meaning you can easily clip the output of your UAD plug-ins and not even know it. Because UAD powered plug-ins run as wrapped RTAS, you will not see clip indicators like you normally do with TDM plug-ins (plug-in insert lights up red). Internally, the UAD system is processing at a 32-bit float precision, and the emulation algorithms are designed in a way that allow you to "push things beyond zero" to achieve the signature sound of a particular unit in overdrive. This is all fine and good until you hit your next TDM insert, which truncates the output of the UAD plug-in back to the legal 24-bits. Without getting into an overly complex discussion of DAW mixer headroom and Native vs. TDM insert chains, just know that you need to pay attention and use the UAD plug-ins output trim to bring the plug-in back below 0dBFS before hitting the next signal processor in the chain. I use pre-fader metering to make sure my plug-in chains are behaving nicely and remain below 0dBFS from insert to insert (Options > Pre-Fader Metering). If you use Pro Tools LE/M-Powered all you really need to do is pay attention to is your master outputs (e.g. A1-2) master fader. Since this mixer is 32-bit float through and through, you just need to make sure you aren't clipping your converters at output.

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