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Dolby SDU4 Hardware Dolby Stereo/Surround decoding
(2017-12-08, 06:21 PM)Jetrell Fo Wrote: @Tom,

You certainly have gone far for headphone mixes.  I hope it all works out well for you.


Thanks! So far I'm loving it. Smile
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This is all kind of freakin' awesome!
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Well, this is awkward. I've not initially noticed it, but I had a crazy amount of noise in the surround channel in all my decodings using this unit. And I always had to record with the output level set to the absolute maximum.

I knew it couldn't be a fault of my audio interface as it is a very good one by a good company and there is no audible and barely measurable noise at all without inputs attached. Also, the signal lamps on the SDU4 would barely ever light up properly.

Initially I thought my unit may just be defective because the noise was mainly in the surround channel and the others sounded fine. Well, according to the manual the surround channel has a dynamic range around 10 dB smaller than the other channels, so that didn't seem too weird after all, BUT even the surround channel is supposed to have a dynamic range of greater than 70 dB and that definitely doesn't seem like what I was getting.

Well, turns out I had it calibrated wrong. You're supposed to calibrate it with a reference tone, which I assumed was simply a signal at full volume on the computer, that is 0 dB.

Turns out, a reference signal is understood to mean something around -20 dB (!!). Well, needless to say, after turning the calibration screws a felt dozen times to the right side to get the correct calibration at -20 dB, my noise issue was gone and everything sounds crystal clear now. Smile

So anyone I've done decodings for, let me know if you want me to redo them with 20 dB less noise!
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