Dolby SDU4 Hardware Dolby Stereo/Surround decoding

[deleted user]

@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.

[Stamper]

This is all kind of freakin' awesome!

[deleted user]

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.

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

[spoRv]

Don't know if could still be useful, but just found the manual:
https://audiorents.com/library/userManua...y_SDU4.PDF
there is no sign of Pro-Logic in the manual, still in brochures it is there:
http://www.advancedaudiorentals.com/docs...20SDU4.pdf
https://mpe.berklee.edu/documents/studio...DU%204.pdf
can't say if it's analog - can someone take a look at the manual?

[deleted user]

I'm 99.9% sure it's analogue. It's a very old unit, made before 1990.

[spoRv]

You know what? Found one here for 15€... should I get it? (rethoric question, by the way! )

[deleted user]

If it works, go for it!

[spoRv]

I'll post here if I'll get it - still, can just understand if it will switch on, though!

According to this book, it is analog: https://books.google.lt/books?id=OptdlsL...22&f=false
Good!

[deleted user]

It's a nice unit, hope it works out for you. Don't forget to study the manual about the proper calibration etc. so you don't make the same mistake I did and end up with too much noise.

[spoRv]

It's a nice unit, hope it works out for you. Don't forget to study the manual about the proper calibration etc. so you don't make the same mistake I did and end up with too much noise.

When I would be able to actually use it, I'll ask you advices!