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Pro Tools: Integrating Outboard

Avid Pro Tools Tips & Techniques
Published November 2017
By Mike Thornton

Before and after: renaming my hardware inserts to reflect what they’re connected to makes life a  lot easier.Before and after: renaming my hardware inserts to reflect what they’re connected to makes life a lot easier.

Bring a new dimension to your Pro Tools mixes by integrating outboard hardware.

In this month’s Pro Tools workshop we will be looking at how to integrate hardware effects units into Pro Tools and use delay compensation to adjust for any latency involved in sending signals to and from them.

Although most of us are doing more and more ‘in the box’ these days, using plug-ins for processing, plenty of people also want to use hardware effects units and processors within their Pro Tools mixes, either because there isn’t a plug-in equivalent or because the hardware just sounds better. The good news is that the Avid Audio Engine introduced in Pro Tools 11 has streamlined the use of delay compensation, which is vital when you’re using your interface to route audio out to a hardware processor and back into Pro Tools. But before we get into all that, let’s look at the mechanics of getting an outboard dynamics processor and reverb unit hooked up to Pro Tools.

Matching Inputs & Outputs

When using your interface I/O as insert points for hardware units, it is essential that you use matching numbered inputs and outputs. For example, if you want to send audio to a hardware compressor on output 5, the output of the compressor must come back into Pro Tools on Input 5. This is because of the way the Inserts tab of the Pro Tools I/O window is configured; you cannot configure insert send and returns to be on non-matching I/O. I always prefer to label my inputs and outputs, and naming them according to the devices that are routed to those inputs and outputs saves me having to remember what is connected to what. Outside In

Hardware insert points can be named in the Insert tab of the Pro Tools I/O window. In the screenshot, I am going to allocate channels 5 and 6 on my HD I/O for use with my hardware EQ. Double-clicking on the stereo insert will enable me to label them both at once: in this case I am renaming ‘B 5-6’ to ‘Hardware EQ’. The mono sub-paths, accessed by clicking on the little triangle, will be automatically renamed ‘Hardware EQ.L’ and ‘Hardware EQ.R’, but I can use the same process to rename them ‘Hardware EQ 1’ and ‘Hardware EQ 2’.

To use a hardware insert, click on one of the insert points on a track, but instead of selecting a plug-in, go to the bottom of the list and choose I/O. You will see all the interface I/O that can be used for inserts. In this screen, you’ll see that the two options B1 and B2 are yellow, which means those inputs or outputs are in use in the current session. You will also see the two renamed inserts Hardware EQ 1 and Hardware EQ 2.

Once set up, hardware inserts are available from the same menu that’s used to select plug-ins.Once set up, hardware inserts are available from the same menu that’s used to select plug-ins.Note that a hardware insert does not have a bypass button — bypass buttons for plug-ins are actually part of the plug-in, not the mixer insert. If you want to bypass a hardware insert, the way to do it is to make the insert inactive: right-click on the insert name and choose Make Inactive. The hardware insert name will be italicised and the insert on the track will be greyed out. To bring the hardware insert back into action, right-click again and select Make Active.

When using auxiliary effects units such as reverb and delay, there’s no need to match hardware inputs and outputs unless you want to use them as inserts, as described above. You can simply send from source tracks directly to the hardware output that feeds the reverb, and use an aux track as an effects return, picking up the inputs to which the reverb’s outputs are connected.

Delay Compensation

Sending audio to and from an external processor takes time. The audio has to travel out of the interface’s output buffer and D-A converter, through the hardware processor, back through the interface’s D-A converter and input buffer and into Pro Tools. The first and last sections of that journey will be the same in every case, because they are down to your interface setup, and Pro Tools will compensate for them automatically. However, some outboard units — including all digital devices — will add a latency of their own, which needs to be compensated for. The best way to do so is to measure the round-trip latency yourself, and I am going to show you how I do this in Pro Tools.

Before you start, make sure that Automatic Delay Compensation is switched on in the Options menu. If you are using Pro Tools 10 or earlier you will also need to choose Short, Long or Maximum; from Pro Tools 11 and above, that option is no longer required. Set your Session’s Main Time Scale to Min:Sec. Create two mono audio tracks and record a short section of tone on the first. The way I do this is to highlight a 50ms section of the track, select Signal Generator from the AudioSuite menu and hit Render — but you could use any audio sample, as long as you can clearly identify the start of the audio.

Next, add a hardware insert on this track, as described above. In this example I am going to use input and output 5 from my HD I/O, which I have labelled ‘Hardware EQ 1’.

Set the hardware processor up so that only the dry signal is being passed, but don’t put it into a true bypass mode, as the audio needs to go through the full chain, including any delay introduced by the processing. In the case of a compressor, set the controls so that it doesn’t compress, and for an EQ, set the controls flat. In the case of a reverb or delay, setting the output to 100 percent dry will ensure that the audio passes through the processor, but the effect won’t mess up the test measurement.

Now bus the output of this first track to the input of the second track. Select the clip on the first track so that recording is only enabled for the duration of this clip. Record-enable the second track, then press Record Enable and Play in the Transport window. Pro Tools will play back the audio on the first track and record it, via the outboard processor, to the second. Measuring the latency of an external hardware processor: the offset between the original and the re-recorded signals represents the time delay introduced by the processor.Measuring the latency of an external hardware processor: the offset between the original and the re-recorded signals represents the time delay introduced by the processor.

After recording, zoom in and measure the difference between where the audio starts in the two tracks. The way I measure the offset is by placing the cursor at the start of the audio waveform on the second track and then using the keyboard shortcut Alt+Shift+Tab. Assuming you only recorded for the duration of the first clip, as described above, this will take the cursor back to the beginning of the clip, thus selecting the offset between the starts of the sound in the two clips. The selected area represents the time difference between the two clips and hence the delay introduced by the insert processing on the first track. You can then read off the length of this selection; be aware that the timeline display doesn’t show time increments less than 1ms, so I suggest you look at the time ruler when you are zoomed in to measure the offset accurately. We can now enter this figure into the H/W Insert Delay tab in the Pro Tools I/O Setup window: in my test case, the delay was around 1.75ms.Once I  know the latency of a  hardware processor, I  can enter it into the H/W Insert Delay field and Pro Tools will automatically compensate for it.Once I know the latency of a hardware processor, I can enter it into the H/W Insert Delay field and Pro Tools will automatically compensate for it.

Once you’ve figured out the delay and entered it, the delay compensation engine will compensate for the latency of the external processor as well as the round trip out and back through a hardware insert point, and you can use your favourite hardware processor in your Pro Tools Session without having to move clips backwards and forwards to compensate for the round-trip delay.

Thinking Outside The Box

Not all Pro Tools users have conventional outboard processors to hook into their systems — but don’t forget the possibilities involved in sending sound through guitar pedals, and with more and more sound-mangling tools available on the iOS and Android platforms, you might choose to use this as a way of harnessing these low-cost platforms. You need to have an audio interface of some kind for your smartphone or tablet, but then you can use the apps to process your audio, making full use of the touchscreen interfaces that can bring some of those effects to life.

Published November 2017