Topic: S/PDIF Volume Levels | Allen & Heath Digital Community

S/PDIF Volume Levels

This topic contains 2 replies, has 2 voices, and was last updated by brandonhw 13 years, 6 months ago.

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2010/10/04 at 7:27 pm #22495

brandonhw
Participant

I’ve had some issues connecting S/PDIF gear to my T-112 surface. It seems the levels between my outboard gear (CD recorder, player, and M-Audio USB interface) do not match. For example, if I test with pink noise at 0 dB at the B?-7/8 output, it shows a full zero dB on the meter, but at my computer or CD recorder, I am barely getting a signal (probably less than -30dB), but on the other hand if I send a S/PDIF signal to either the A-7/8 or the C-7/8 input on the surface and send 0dB pink noise, I have to trim it all the way down, and it’s still too strong.

It seems that there’s a mismatch between what point of reference there is for audio levels. I can compensate by trimming the input, but I have little or no way to adjust what comes out. I’ve got my computer inputs all the way up and can’t get a usable level.

Any suggestions?

Brandon

2010/10/04 at 11:46 pm #26571

ZiKE
Participant

This difference is caused by different dB values used in iLive and computer recording programs. Remember, that dB is not an unit. It is only a suggestion, that measured values are shown logarythmically. iLive scale is just in dBs where 0dB on meter means +4dBu on output. It is scale typical for analog consoles. Maximum output level without distortion is about +22dBu, so it is 18dB on scale. Your computer shows values in dBFS (Full Scale) where 0 dBFS means the maximum value (which can not be exceeded in any way).
It means, that when you’re sending 0dB (dBFS) from your computer it is also a full signal in iLive, 18dB above 0 on meter. And when you’re sending 0dB from computer via S/PDIF you will get -18dBFS on your computers scale.
Of course real values can vary from those above, your recording program can show RMS value despite peak (few dB lower), I am also not sure is 0dB in iLive exactly +22dBu on output.
Please look for dB, dBu, dBV and dBFS.
Best regards,
ZiKE

THERE IS NO JUSTICE, THERE IS ONLY ME

2010/10/11 at 11:15 pm #26614

brandonhw
Participant

quote:

Originally posted by ZiKE

This difference is caused by different dB values used in iLive and computer recording programs. Remember, that dB is not an unit. It is only a suggestion, that measured values are shown logarythmically. iLive scale is just in dBs where 0dB on meter means +4dBu on output. It is scale typical for analog consoles. Maximum output level without distortion is about +22dBu, so it is 18dB on scale. Your computer shows values in dBFS (Full Scale) where 0 dBFS means the maximum value (which can not be exceeded in any way).
It means, that when you’re sending 0dB (dBFS) from your computer it is also a full signal in iLive, 18dB above 0 on meter. And when you’re sending 0dB from computer via S/PDIF you will get -18dBFS on your computers scale.
Of course real values can vary from those above, your recording program can show RMS value despite peak (few dB lower), I am also not sure is 0dB in iLive exactly +22dBu on output.
Please look for dB, dBu, dBV and dBFS.
Best regards,
ZiKE

THERE IS NO JUSTICE, THERE IS ONLY ME

Thanks for that ZiKE. While I understand the differences in scales, I really don’t have a usable volume level at my computer from the iLive. It is quite um.. quiet. Even when I have every level control at full, I’m getting an audible, but not fully usable signal into my computer, yet every other S/PDIF piece of equipment I own will produce a full signal.

The reason this is such a big deal to me is that I am doing a live streaming broadcast and I was trying to keep it digital. It works fine if I use an analog output. I even tried running the S/PDIF output into my CD-recorder, with the same result. Two different recorders (one couldn’t work with the bitrate, and created a CD that sounds slow when played back, but still had the low levels). Since the iLive is the odd one out, then that’s what I’m looking at as part of the problem.

Brandon

Brandon Walls
Sound Engineer
First United Methodist Church
Cookeville, TN
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