Bit Perfect audio and auto-switching with the M-Audio Transit USB


Found some information regarding M-AUDIO's USB Transit which may be of interest to some. Using the Transit is one method that allows you to bypass Window's K-Mixer so that music isn't upsampled to 48Khz. Previously, the downside to the Transit was that it didn't switch between AC3/DTS passthru mode and plain old PCM automatically, you had to manually change the mode in the Transit's control panel. This can now be overcome:

You need to use the older drivers for the Transit, v1.0.22. Download

You need AC3Filter, I'm using 1.07a, which works. Haven't tried the later versions but they'll probably work too. Download

Set the Transit to 2in, 2out, 16-bit, 8000 Hz to 4800 Hz in it's control panel app.

In AC3 filter, check "Use SPDIF" on the Main tab and "Output SPDIF as PCM" under SPDIF options on the System tab. Also tick what formats you want, which will probably be all of them.

This last step is if you're using the Purevideo decoder and MCE. You need to force MCE to use the AC3Filter codec by changing the following registry key:

Go to start -> run -> regedit.exe
Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion \Media Center\Service\Video

Change PreferredMPEG2AudioDecoder by replacing the value with this one:

Reboot and you should now have the Transit auto-switching between AC3/DTS and PCM.

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