Reducing volume?

[barendh]

Is there any way to reduce the volume in a digital stream?
I've been thinking about this a lot, and can't think of anything...
I mean streams like optical (Toslink) or coaxial feeds...
Thanks for thinking

[suspencefull]

Coaxial and Tosilink are digital streams. There is no volume in them. When they are switched to analog this is when volume information is added. I may be wrong though. That case someone correct me.

[anatech]

Hi barendh,
Yes. You would decode the digital stream and adjust the volume (DSP), then re-encode the stream and send it on its merry way.

Somehow it doesn't seem worthwhile. Even adjusting the level will create long digital words that you have to truncate.

-Chris

[clem_o]

Originally posted by suspencefull
Coaxial and Tosilink are digital streams. There is no volume in them. When they are switched to analog this is when volume information is added. I may be wrong though. That case someone correct me.

The digital stream already has the 'volume' encoded, it's not added later in analog. The amplitude is represented as a number (ok, numbers), encoded as a binary stream.

It's the job of the receiver of the digital stream to reassemble the stream into their proper groups (words), pass this to the digital to analog converter, which takes the binary numbers and converts them into an analog form (usually a current), from there it becomes a varying (analog) voltage.

Changing the volume can happen in several places - the DA converter can be 'told' to increase or decrease the factor of conversion from binary numbers to current; the current to voltage converter gain can be changed, or the binary numbers can be manipulated (through appropriate digital circuits, such as a DSP mentioned by anatech, or simpler circuits (but still digital anyway).

In other words, well, it's practically not possible to do it in the toslink or coax stream.

Cheers!

[barendh]

Thanks guys,
I was afraid of that...
You see, my set top box toslink output blows my ears inside out when I switch from analog inputs to TV...
On my current 990 Outlaw Audio processor that is.
Next week I'm getting a 2nd hand Arcam AV8 multichannel preamp on trial that is said to have a per channel max volume setting.
But I'm not getting my hopes up too much, since that only worked for the analog inputs as I remember from the Arcam A85 stereo amp I once had...
Agree there must be DA'ing at SOME point, and if all fails I'm gonna hunt for that point inside the Arcam (or Outlaw) !
Barend

[AndrewT]

Hi,
it sounds like your audio connector box is decoding the Toslink signal at the full analog Vmax =2000mV, without any attenuation.

You need to intercept the analog signal after the decoding/DAC and attenuate the signal to the same level as the other sources.

You are right about the AV8, the presetable sensitivities applies to the analog inputs.
The AV8 works like a conventional pre-amp, it attenuates all the inputs in the analog domain before outputting the signal to your power amp.


Your Outlaw should be consigned to the bin.

[clem_o]

It would seem that the easier solution would be to UP your analog source signal(s) - particularly easy if there's only one other analog source you often listen to...

Cheers!

[AndrewT]

Hi Clem,
not if the digital signal bypasses the attenuator.

[clem_o]

Hi Andrew - not sure I followed you there...

Barend's problem is that his digital input source sounds 'much louder' than his other sources (which I take are analog, i.e. FM stereo, LP, or analog CD playback - and oops, there he says 'analog TV') - and when he switches from analog input to digital, he gets an earful of sound.

So, the easier thing to do here will be to amplify the analog TV signal, so that he doesn't have to play with the volume control when switching between analog and straight digital source...

Ah, hang on, yes, I think I understand what you mean... silly me.

I was assuming that whatever happens, the 'main' volume control of his system would always work to attenuate volume. OTOH I have to admit I don't know what the 'Outlaw' nor Arcam internal config is...

Cheers!

Clem

[AndrewT]

Hi,
the mention of Arcam made me look back to the AV8 reference.

OOPS, my comment about level setting and attenuation applied to the Cyrus AV8, I have no experience of the Arcam AV8.