ADC Total Weirdness.

[25ghosts]

I have measured the H/W insert delay that my converters and outboards are producing.

This is exactly 121 samples and in a a 96KHZ this is exactly 121 / 96000 * 1000 = 1,260416666666667 MS rounded that brings me to 1.26 Milliseconds.

Now according to the digi manual this value is what I am supposed to enter in the H/W insert delay field... So that is what I do.....

Here comes the weird part. When inserting the I/O in the insert of an audio track - 121 samples of delay is NOT applied to that track. Instead PT applies 205 Samples - which are 2.14 MS in 96 KHZ session..... What is up with that....

If anyone can explain this to me - I'm buying a cappuccino.

Thanks

[25ghosts]

I Think I may have found the BUG....

I have four Rosetta 800 interfaces connected to my core card via daisy chain thus I have 32 I/O's

Channel 1-8 get 205 samples applied to then when entering the 1.26 Milliseconds value
Channel 9-16 get 133 samples applied to then when entering the 1.26 Milliseconds value
Channel 17-24 get 05 samples applied to then when entering the 1.26 Milliseconds value
Channel 25-32 get 133 samples applied to then when entering the 1.26 Milliseconds value

Now I dont know if this is an Apogee issue or PT's....

However it may be - this is an important bug in either of them - I will contact Apogee about this...

In the meantime it would be cool if someone else could test this


Thank

25

[25ghosts]

Seems this problem is NOT only with Apogee interfaces...

I downloaded the X-HD Firmware update and it changed the values I reported earlier - in the right direction only NOT the correct values...

So I tried it with digidesigns 192 digi i/o - it is reporting WRONG values - even after firmware update...

It is easy to reproduce:

1 - Open a session and set it to 96 KHZ
2 - Go to I/O Setup and select the H/W Delay pane.
3 - Enter the Value of 1 (One) Millisecond for the desired I/O Delay.
4 - Insert the I/O on an audio track
5 - PT will compensate the digital 192 I/O with 205 samples

It should only compensate with 96 samples - as 1 millisecond at 96KHZ is equal to 96 Samples...


Is this a BUG - or am I loosing it...

Thanks for replies

[Top Jimmy]

Also consider that the ADC engine is compensating for the delay incurred in both the D/A and A/D converters. Don't input any manual delay compensation value and you should see an ADC value equal to the total value you saw minus the manual value that you put in.

Now here's where the fun for you begins. The Rosetta does not have conversion values identical to a 192. If you really want to compensate precisely, you're going to have to figure out the difference in delay between the 192 and Rosetta and take that into consideration when you enter the manual compensation value. Otherwise, your tracks with hardware inserts are not really going to be compensated properly.

[Akat-1]

I thought with the latest firmware the Apogee interfaces don't have the latency issues that they used to? Has anyone done any tests to confirm this..

[Top Jimmy]

The firmware update allows X-HD carded interfaces to be seen by Pro Tools as 192 Digital interfaces. This means that all 16 channels have identical delays rather than 1-8 and 9-16 having different delays when it appeared as a 192 interface. Even so, Apogee interfaces have longer conversion delays when compared to both the 192 and the 192 digital. This means that any hardware insert through an Apogee interface has to have an additional amount of manual compensation entered to compensate for the additional conversion delay. Don't ask me the values, I never actually documented them when I measured. Our workflow doesn't require knowing these values since all the mixing outputs are through Apogee interfaces and external summing. We just make sure all the drum tracks are out the DA-16s without any on the Rosetta since there is even a delay difference between those two different interfaces. Drum tracks shared across the two fall out of proper phase relationship.

[Akat-1]

The firmware update allows X-HD carded interfaces to be seen by Pro Tools as 192 Digital interfaces. This means that all 16 channels have identical delays rather than 1-8 and 9-16 having different delays when it appeared as a 192 interface. Even so, Apogee interfaces have longer conversion delays when compared to both the 192 and the 192 digital.

Not that it makes a difference with your setup but I believe the Apogee interfaces actually have less latency than the 192's.

One interesting thing to note is that now when I do an all digital bounce via my Rosetta 800 with ADC on and the option for compensate for input delays checked- the stereo mix comes back sample accurate with the multitrack- which makes me happy...

[Top Jimmy]

Not that it makes a difference with your setup but I believe the Apogee interfaces actually have less latency than the 192's.

Apogee converters have greater amounts of AD/DA conversion delay than does a 192. Check it for yourself. Print a test tone on an audio track, run it out analog on the Rosetta, bring it back in on the Rosetta and route it to another audio track. Make sure that both compensation boxes are checked in the I/O setup window. Print the test tone to the second track. Focus in on the start of the test tone. Do the two tones line up or is the second one shifted ahead or behind?

The reason Apogee publishes the manual compensation numbers is so that you can put them into the H/W Insert Delay Compensation window to compensate for the additional delay of the Apogee converters. But this only applies to using the Apogee I/O for hardware inserts. Any way you cut it, if you use the Apogees while overdubbing, the tracks you record will always be slightly behind where they should be, unless you come up with a workaround. The worst is little more than a millisecond, but in this day and age, precision should be something expected. Should Apogee redesign their converters to have identical delay to a 192, or should Digidesign allow Pro Tools to play nice with third party interfaces?