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Sound Devices USBPre 2 In Stand-Alone Mode
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PowerOutlet
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#1
26th February 2013
Old 26th February 2013
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Sound Devices USBPre 2 In Stand-Alone Mode

After extensive research, I'm on the verge of purchasing a USBPre 2 but need to ensure it's capable of meeting my needs. Hoping someone with experience can help.

For studio use, I want to use the device in stand-alone mode as a mic preamp that will feed Toslink digital into an existing Firewire DAW interface.

I also want to connect the Toslink output of the FW interface to the digital inputs of the USBPre 2 and use its analog outputs for monitoring purposes.

From what I've gathered, I believe operating the USBPre 2 in either of these ways independently isn't an issue. It's designed to meet both needs. What's unclear to me is whether or not it can perform both functions simultaneously. To be clearer...

The block diagram schematic in the USBPre 2's user manual (http://www.sounddevices.com/download...USBPre2_en.pdf ) makes it look as though its digital inputs and digital outputs are internally connected when in stand-alone mode and if this is the case, would there not be an issue with creating a digital feedback loop if -- during multi-tracking / overdubbing -- the DAW is sending its input directly back to the USBPre 2 over Toslink?

Has anyone used the device in this manner? Any experiences to share?

Thanks,
dp
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26th February 2013
Old 26th February 2013
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nnajar is online now
I would suggest you telephone SD tech support. They very friendly and will walk you through it. They have told me it will do just what you ask but I have not tried it so I cannot verify for you.
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27th February 2013
Old 27th February 2013
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David Spearritt is offline
I use the USBPre2 in standalone mode to add two extra channels to my Orpheus. I connect SPDIF in and out to Orpheus out and in and can record the signal fine. The Orpheus out to USBPre2 SPDIF in is only there to establish a clock locking for the USBPre2 to the Orpheus.
PowerOutlet
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27th February 2013
Old 27th February 2013
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David... Thank you. That sounds promising. I've actually lobbed a call into SD support as well -- they're looking to create a test set up to confirm the USBPre 2 behaves they way they believe it should.

If I may ask... Are you monitoring (i.e. for overdub purposes) out of your Orpheus?

Thanks,
dp
PowerOutlet
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27th February 2013
Old 27th February 2013
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Hey All,

Below I'm copying the correspondence I've had with Sound Devices support this morning. Per results of their testing, what I'm looking to do won't work due to creation of a digital feedback loop. I hope this information will benefit others.

If anyone has had an experience that differs from SD's, please let me know.

Cheers,
dp

============================================================

Dear SD Support Team,

I'm in the process of deciding on a new digital pre-amp for my home studio and the USB Pre 2 has made the short list. I've reviewed the User Manual and read far more online reviews than are recommended by the FDA. I feel I have a solid grasp of the features of the interface and the available configuration options.

I understand the device functions as a full-fledged USB audio interface and it will likely see some mobile use in this capacity. However, its main use will be in stand-alone mode as a front end to an existing Firewire audio interface. My plan is to connect to the FW interface over S/PDIF effectively bypassing the preamps, D/As and A/Ds on the interface. All good.

One piece, however is unclear to me. If I connect the USBPre 2 to my interface over S/PDIF in both directions (i.e. input and output) so I can monitor via the analog outs on the USBPre 2, is there any risk of creating a digital feedback loop during recording / overdubbing (i.e. is the device's S/PDIF input looped back through its S/PDIF output)?

To be (a little?) clearer, the set up will look like this:

As Input Device: Mic -> USBPre2 -> (Over S/PDIF) -> FW Audio Interface -> DAW Software

As Output/Monitoring Device: DAW Software -> FW Audio Interface -> (Over S/PDIF) -> USBPre2 -> Amp -> Monitors

I see how the device would work in one or the other of these capacities (or both at different times) but can it be used in both capacities simultaneously in stand-alone mode?

============================================================

Hi David,

We were able to use a set up like this and there was digital noise induced due to the loop through. What kind of FW interface are you using? If it is working as a control surface There may be a way around it if all audio is handled through the USBPre 2 and the FW interface is used as the controller. However if the FW interface is just an audio I/O device it will not work.

============================================================

Hey, Casey... Thanks for your response.

My audio interface is an M-Audio FW410 -- old but stable with solid drivers. This device is purely an audio I/O device -- not a control surface (i.e. it does carry MIDI data, however but that shouldn't interfere with S/PDIF).

If I interpret the situation correctly, in stand-alone mode I should be able to monitor audio from the DAW as long as the DAW itself isn't looping a copy of that data back to the USBPre 2 through the interface (i.e. in which case the USBPre 2 -- because its S/PDIF input and output are internally connected when in stand-alone mode -- would create a digital feedback loop.)

Does this sound correct?

============================================================

Hi David,

Your interpretation is correct. As long as the DAW isn't sending a copy back to the USBPre 2 it would work.

============================================================
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