Join David Franz for an in-depth discussion in this video Utilizing ADC while mixing, part of Pro Tools 10 Essential Training.
In this video I want to talk about using Automatic Delay Compensation. Host-Based RTAS and AAX plug-ins, as well as HD-only TDM plug-ins, are all real-time effects. It takes a little time for your computer to process the audio signals that pass through them. This processing delay can be measured in number of samples or milliseconds, and it can add up to a significant amount of time. Now some plug-ins, like the stock EQ plug-ins in Pro Tools, require very little processing power and have zero delay.
However, processor-intensive plug-ins like pitch-correction plug-ins, long delay effects, look-ahead mastering limiters like the maxim plug-in, and noise- reduction plug-ins can have much larger delay times. For example, one instance of the maxim plug-in has 1024 samples of delay, and the delay literally adds up. The total delay of a track is equal to the sum of all the delays from all the plug-ins on that track. So if you have three maxim plug-ins on one track, that's going to cause over 3000 samples of delay.
Now let's listen to this example. First I'm going to play back the track with no delay, and we'll hear what it sounds like. And you'll see that I actually have two acoustic guitar tracks here. These are double-tracked, two different guitar performances but played in time with each other. (Music Playing) Now you notice that they both have EQ plug-ins on them, and I'm going to bypass this one, and I'm going to play it back, and we'll see if you can hear any delay.
(Music Playing) The two tracks are very tight still, because the EQ plug-ins don't cause any delay. However, I want to make these maxim plug-ins active now, so I have three maxim plug-ins, and now let's hear the difference between the left and the right side of this guitar track. (Music Playing) Now we can obviously hear the difference in timing, because this track is playing back over 3000 samples later than this top track.
To combat delay, Pro Tools can add the same amount of delay to each track, and this is called automatic delay compensation. So if I go up to the Options menu here and come down to Delay Compensation, I'll choose that, and Pro Tools wants this to open up the Playback Engine dialog in order to enable this, so I'll click OK. In the middle of this dialog box you'll see the Delay Compensation Engine, and it's set to None right now. If I click this, we have three other options: Short, Long and Maximum.
The Short setting allocates the smallest amount of resources for ADC, or automatic delay compensation, and this is more efficient than the long and maximum settings for our computer. And we can use this smaller value when we don't have very many plug-ins or if we know that the delay is less than this number. I can choose Long to allocate more resources to ADC, and we should use this when the session requires more than the short amount, but not the maximum. And then the maximum, which is quite a large number, we can choose this and we'll get over 16,000 samples per channel.
Now you should note that these ADC values differ depending on the sampling rate. If you double the sampling rate, say from 48 kilohertz to 96 kilohertz, the number of samples for ADC will also double, but both settings are equal to the same amount of delay compensation. So this session right here is actually a 44.1 kilohertz session. If we were to double this to 88.2, we would see twice as many samples here, but it would actually equal the same amount of time.
So I'm going to choose the Long setting. And Pro Tools is asking us whether we want to proceed here, which means that we need to close the session. And it'll save automatically--go ahead and do that. So it closes the session, and then it needs to reopen with the delay compensation on, so I click OK and here we have it reopened with the automatic delay compensation on. Now there is a way to check how much delay compensation is needed, and that is here in the Mix window down at the bottom. And to show that if you don't see it, we go to View > Mix Window Views > Delay Compensation.
So you can see on this track with the EQ, we have 0 delay. However with the maxims, we have three maxim plug-ins here, and that's causing over 3000 samples of delay. You'll notice that the color down here on this track is orange, and that means that delay is enabled, and this track has the longest delay of all the tracks in the session. The green tracks mean also that delay is enabled, but we're not exceeding the ADC level on these tracks and they're not the maximum track like this one is.
When the amount of delay exceeds the ADC limit then this is going to turn red. So what happens if we add this last maxim in here? And you'll see that this exceeds our maximum amount, and that number is actually 4095, so we're over by one sample here. Down here on each of the tracks, you can see that these are actually being compensated by 4095 samples. So that's to push them back so that they line up with this track.
Now below the Delay indicator here we have a user offset, and that enables us to manually adjust the ADC if we want to add in a user offset, and the only reason we do this is if it's not sounding quite right because maybe the plug-in is incorrectly reporting the delay amount or if you just want to manually adjust the timing or the feel of the track. And here you'd enter a positive number for more delay compensation or a negative number for less.
If for some reason we want to hear with this track sounds like without the delay compensation, you can press Start+Ctrl+Click in Windows or Command+Ctrl+ Click on Mac on the user offset, and that will turn off the user offset. And if you click on the delay then that will turn of the delay. There is another way to deactivate the delay compensation. If we go up to Options and uncheck Delay Compensation, that turns it off, as you can see down here. We'll turn it back on.
Now in addition to accounting for delays caused by plug-ins, automatic delay compensation also accounts for delays in internal mixer routings, due to using buses and sends, as well as from hardware inserts, and this is called the System Delay. If we go up to Setup > Session, we can see here that the total system delay is actually 4146 samples, and that's a little bit more than what we have down here. In fact, it's 50 samples more than what the plug-ins cause.
So what do you do if your total delay on a track exceeds your ADC limit? Well, it's pretty simple here. If it's set to Short then you should choose Long, and if it's set to Long then we can choose Maximum. So in this case we would actually go to the Playback Engine and choose Maximum and click OK twice. We'll open this up, and you'll see now that this is set to orange, so we're not exceeding our maximum level anymore.
If somehow you end up exceeding the maximum, you should just bypass this and actually physically move the track. So if we go back to the Edit window-- so we can literally click and drag this track and manually nudge the audio data on the track earlier in the session by the amount of delay time reported in the track's Delay Indicator, and we can get specific about that by zooming in and taking a look at that, but we're not going to cover that here.
So Automatic Delay Compensation is a great feature and can really help to make your mixes sound more accurate and time aligned. I recommend activating ADC every time that you play back a session in Pro Tools, and most importantly, when you're working on a mix.
- Exploring the Pro Tools interface
- Selecting inputs, outputs, and busses
- Understanding signal paths and gain stages
- Setting up Pro Tools hardware and software properly
- Importing audio from multiple sources
- Recording and editing audio and MIDI
- Adjusting time, tempo, meter, key, and chord in arrangements
- Mixing and mastering a session
- Setting up an effects loop
- Importing and displaying video
- Adding music, Foley, ADR, and FX
- Archiving a session