The use of Apogee interfaces with Delay Compensation complicates the calculation for two reasons:

1. Apogee conversion is, in some instances, faster than the conversion in a Digidesign interface.
2. With a pair of Apogee interfaces, the user typically has a 16x16 analog interface per port where with the Digidesign 192 (the interface that every HD-compatible Apogee appears as), only 16x8 or 8x16 per port, is possible.

The compensation process basically amounts to identification of the track with the longest delay and the interfaces which are in use, followed by adjustment of each output. 

As with Digidesign interfaces, the throughput delay of an Apogee device is a constant value. Therefore, knowing the Apogee delay constants as well as how Pro Tools compensates for a 192 is enough information to make the minor changes needed to use Delay Compensation with Pro Tools.

To simplify the process of using Delay Compensation with Apogee interfaces, Apogee provides the Delay Compensation Adjusted Latency Calculator, or ADCALC. ADCALC may be used to determine what sort of adjustment is necessary when a digital or analog insert is used on a session. ADCALC provides a number (in samples) that is based on the Apogee units in use, the sample rate of the session, and the insert channel(s) in use. Depending on whether the output number is positive or negative, the ADC adjustment may be accomplished by one of two methods:

• Entry:
  Entering an additional delay value in the Delay Compensation portion of the Mix Window

- or -

• Nudge:
  Shifting backwards in time the position of the audio present on the channel with an insert.

It is, unfortunately, not possible to manually adjust via the Mix Window in all cases as Pro Tools does not allow for “negative” delay adjustment.

Below is an example of the two types of manual adjustment using ADCALC

Note: Before beginning to work with any xHD equipped Apogee equipment, it is recommended that the user “Set to Default” the settings on the Hardware Setup page and on each of the I/O Setup pages (Input, Output, Busses, etc). Additionally, in order to use Delay Compensation, it must be turned on from the Operations menu. To make some of the adjustments (as described below), the Delay Compensation View must be enabled from the Display pull-down menu (Display -> Mix Window Shows -> Delay Compensation View).

• System: Apple PowerMac G5 running Pro Tools 6.7
• HD – 1 w/ AD/DA-16x connected (appears as 192 with 8x8 analog, 8x8 digital
• Sample Rate: 48k

The example session contains only two tracks of audio: a stereo track of drum overheads and a stereo track of room mics. The first example involves inserting an analog compressor on the overhead mics. Since the input and output A7-8 are currently not in use, we use A7-8 for our analog insert. In the Delay Compensation view, three values are displayed: the delay incurred by the hardware insert, a manual adjustment value (only this may be changed), and the compensation value (see EXAMPLE 1). With out current session, delay incurred (93 samples) and the automatic adjustment to the other tracks is the same.

Using ADCALC, we select the connected interface (AD/DA-16x), the sample rate (48k), and the bank of the insert channel (1-8). The value returned is 24 samples. Since the value is positive, we make the adjustment simply by entering the value in as the manual adjustment value in Delay Compensation view of the Mix Window (see EXAMPLE 2). The manual delay is necessary in this case as the delay value that Pro Tools expects in this instance (93 samples) is actually 24 samples greater than the throughput delay of the AD/DA-16x.

Now, if for some reason we needed all of the outputs A1-8 for something else (i.e. 5.1/7.1 surround mixing), we would use channels A9-16 for inserts. If we enter this change into ADCALC, we note that the output value is now negative. The negative sign signifies that the adjustment must now be made by moving backwards in time (or “nudging”) the audio present on the track with the insert. As explained above, the difference in adjustment method is due to the fact that negative delay values are not supported in the Delay Compensation view.

With Pro Tools 6.7, nudging by sample value may be accomplished very simply. Pro Tools initially boots with the numeric positional reference (located at the top of the edit window) referenced to minutes and seconds. The reference setting must be changed to samples in order to perform a “nudge” in samples. The nudge reference must also be changed to samples via a drop down menu to adjust in samples (see EXAMPLE 3).

To perform a nudge, enter the value obtained from ADCALC (in this case, the value is 55), select the audio sample on the track with the insert, and hit the “-“ (minus) key to nudge the sample backwards (see EXAMPLE 4 for the result). With this adjustment, the track with the insert will now be time-aligned with the adjacent audio track (the room mics).

Note: The values obtained from ADCALC are valid when a unit pair (2 R800s, for example) is attached as either the primary or expansion unit. The values are not accurate when the R800 is setup for digital inserts.