Gaps of 512 samples every 2.5 min

[John Link]

I am getting gaps of 512 samples every 2.5 minutes (2:26 to 2:34) when I record digitally from my Roland VS-880EX through my Edirol UA-3 which is connected by USB to my Cube running OS 9.2.2. I have disconnected the ethernet cable, and I am using an extension set that consists of the OS 9.2.2 base set, less extensions for Printer sharing, Appletalk, TCP/IP, Mac TCP DNR, time synchronization, and internet connections, plus three extensions needed by Pro Tools. When I double the size of the DAE playback buffer I get the same results.

I have done some tests that show that neither the VS-880EX nor the optical cable are creating the gaps. (I bounced a ten-minute sample from the VS-880EX to a DAT deck and then bounced twice from the DAT deck to PTF. Both of the bounces to PTF showed gaps, but none of the gaps were in both bounces.) So the trouble must be in the UA-3, my Cube, or the firewire drive to which I am recording. The UA-3 is connected to a USB port in the bottom of the Cube.

Do any of you have any idea what might be happening every two and one half minutes that would interrupt my bounces?

[M.Brane]

USB is very CPU dependent.

I don't know of any way to monitor CPU usage in 9, but that doesn't mean it can't be done. I've just never really looked into it.

Too bad you can't try a PCI card. Perhaps a FW audio interface or even a different USB device? Maybe even try recording with a different app just to see if it persists.

Is your FW drive freshly formatted, and less than 50% full? Could be an issue there too though I suspect if there was PTF/DAE would throw up some kind of error box.

Do you have find by content enabled? Another possibility.

[John Link]

After doing further tests last night (which I will describe in detail in another post) I have come to the conclusion that there are no external events disrupting my digital transfers, and that digital transfers are bound to have gaps unless the source and target hardware are synchronized with a clock through a midi connection. I'm looking at the UA-25 for $239 to replace my UA-3: http://www.rolandus.com/products/det...prodid=UA%2D25

[M.Brane]

I had considered the clocking issue, but discounted it due to the fact that it shouldn't be a problem when doing a direct transfer. I guess that doesn't mean it couldn't be a problem. A direct S/PDIF transfer shouldn't have clocking issues since the wordclock is transferred along with the audio data. Perhaps it's a cabling issue?

I also didn't know you could clock-sync via MIDI. I thought you needed Wordclock or AES/EBU for that.

[John Link]

Pages 116 and 117 of the Pro Tools Refernce Guide describe how to record from a digital source. There is no mention of a need for using midi for synch, so maybe my conclusion about it was incorrect. As far as I can tell I'm following all the directions on pages 116 and 117, but I still get gaps every 2.5 minutes. One thing that puzzles me is the instruction on page 117 to set the Sync Mode back to Internal after a digital transfer. That puzzles me for two reasons: 1) There was no instruction to set the sync mode to external, and 2) In PTF I am unable to set the synch mode at all, since its window in the Show Sesson Setup menu does not work.

[John Link]

Here's what I did that led me to the conclusion I posted yesterday:

I transferred ten minutes of audio from the VS to Pro Tools FREE through the analog connection on the UA-3. I then repeated that transfer, again using the analog connection. I also transferred that same audio digitally. In Pro Tools FREE I lined up the three transfers so that they would agree to the sample near the beginning of the regions. I examined the two analog transfers near the end of the regions and found that one of them was ten samples longer than the other, which I consider OK given that the discrepancy is only one sample per minute. I then examined the digital transfer and found that it had a gap of 512 samples (.011 seconds) every 2.5 minutes (2:26 to 2:34). I noticed that right before each gap the digital transfer was running about .006 seconds ahead of the analog transfers, and after the gap was running about .005 later. So the insertion of the gaps served to keep the digital transfer approximately in synch with the analog transfers.

[M.Brane]

One thing that puzzles me is the instruction on page 117 to set the Sync Mode back to Internal after a digital transfer. That puzzles me for two reasons: 1) There was no instruction to set the sync mode to external, and 2) In PTF I am unable to set the synch mode at all, since its window in the Show Sesson Setup menu does not work.

I wonder if that's the issue. Maybe PTF is unable to sync properly from the UA-3 (or any other input for that matter) since they only refer to using an 888/24 I/O, and it says that only the first 2 inputs can accept an external clock source.

Wouldn't be the first time PTF was found to be crippled compared to LE/TDM.

[yoursickstudio]

is your sync correct ?
if you play it does it play slower or faster ?
very weird

macos9 is so long ago
but are you only running the extensions you need ?

[John Link]

is your sync correct ?
if you play it does it play slower or faster ?
very weird

macos9 is so long ago
but are you only running the extensions you need ?

I am unable to change the sync mode for PTF, so it must be running Internal, insisting on being the master. It seems that the only external clock the VS-880EX will use is through midi, so it is also insisting on being the master. I think that both PTF and the VS insisting on being the master is the source of the problem. Playback is at the correct speed. For extensions I am using OS 9.2.2 Base plus the few additional extensions needed to run PTF.

John Link

[John Link]

The tests that I have done with Coaster, which runs only in OS 9, suggest that it acts as slave for digital recording. So I can use Coaster transfer from my VS-880EX to my Cube and then use PTF to open the audio files created by Coaster. You can get Coaster here for free: www.visualclick.de

John Link