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Volume Controls WRT Hi Rez Audio


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6 replies to this topic

#1 of 7 OFFLINE   Martin Rendall

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Posted July 12 2003 - 08:55 AM

Here's my claim: most people who have an SACD or DVD-A player connected to their receiver or pre/pro using the typical 6 channel analog inputs are losing resolution. That is, unless they have the right Lexicon or equivalent cost pre/pro.

It's my supposition that most receivers and separate pre/pros do their volume control in the digital domain; there is necessarily a conversion from A-D, volume attenuation, and then back from D-A. This is true even with all the tone controls and BM bypassed. There never seems to be any info published by the hardware manufacturers addressing resolution of such volume controls. For all we know, many volume control systems might be CD quality PCM, or at best, 96KHz. Conversely, if the attenuation is done in the analog domain, how do they maintain good transparency? Hell, a high quality 6 channel mechanical stepped attenuator part will run many hundreds of dollars.

I've read many posts in these forums, and it's clear that people strive to solve their BM issues using analog systems. The Outlaw 950 has analog BM for the 6ch inputs, and the ICBM is a very popular BM solution. Nobody wants to compromise their sound by converting the data to digital for BM, and the back to analog.

Why aren't we all as freaked about volume controls?

If the content has to be converted to digital for the volume control, why not do BM while its here? The loss has already occurred. Why don't manufacturers make the best of it? Maybe I'm missing something.

Comments? Contraditions?

Cheers!
Martin.
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#2 of 7 OFFLINE   Brian L

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Posted July 12 2003 - 09:15 AM

Quote:
Why aren't we all as freaked about volume controls?


For me, its probably because it is completely unclear if what you are asserting is true (converting to the digital domain and back again just to provide level control), and if it was TRUE, I sure as hell don't have a Lexicon budget, so I can't do much about it anyway.

Personally, I would think it more likely that it would be cheaper and less complex to do volume control in the analog domain, rather than muck around with additional A/D and D/A steps.

Do you have circuit diagrams or other real data to support your theory?

And if we are "losing" resolution, is it audible? Can it be quantified? Can it be measured?

I am clearly of the "if I can hear it, it can be measured" camp. So if this is a real issue, then I would expect some data to back it up.

On the scale of things I am worried about, this will not really get much airplay behind screwed up BM, non-existent Time Alignment, etc.

Perhaps someone can contact Outlaw to ask about this WRT their 950? Its the most affordable pre/pro out there, and they have a habit of answering user inquiries.

BGL

#3 of 7 OFFLINE   Scott Oliver

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Posted July 12 2003 - 10:30 AM

Digital volume controls suck.
They only become decent went you get up to the level of the Wadia's or Bel Canto's of the world.

Digital volume control is the number one reason why when I bought my processor 4 years, I got a Theta because at the time (not sure about today) it was the only processor offering analog volume control.

Hence with the Theta, I could turn volume up a few notches up from dead silence and have complete intelligibility of dialog. Digital volume controls throw away too many bits to allow one to do this.

With that said I won't mess with SACD and DVD-A until we have digital connections established, which is why the Theta Casa Nova has not been updated yet as well. They are waiting for digital connections so you can use their superior processing capabilities, compared to all the crappy players floating around out there right now.

#4 of 7 OFFLINE   Martin Rendall

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Posted July 12 2003 - 12:19 PM

Brian,

I'll let the experts chime in about whether the typical mid-fi gear used by most users here has analog or digital volume controls. I have built my own analog equipment, and after much research, I know a fair bit about the issues involved with analog attenuation. Cheaper is relative... as I mentioned, the only decent multichannel stepped attenuator I've run across is a multi hundred dollar part. I also know that nobody who's seriously into tube gear would even consider any sort of digital attenuation.

Now, let's see if anybody can confirm or deny my strong suspicions. Posted Image

I also see your point about it possibly not being as important as BM or TA, or whether you or I would notice any differences. My goal is just to clear up what is going on - not to subjectively judge it.

Martin.
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#5 of 7 OFFLINE   Brian L

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Posted July 14 2003 - 03:32 AM

Martin,

Noodled on this over the weekend, and had a question or two.

I still have a hard time with the overall concept of a true digital volume control in mainstream gear, where there are A/D and D/A steps inserted JUST for that purpose.

What would seem more logical (logic, what does LOGIC have to do with anything?!?!?) to me would be an electronically controlled, (but still analog) volume control.

Again, I have no data whatsoever, but sighting my old school Marantz SR96 Receiver I would offer this bit of conjecture.

The volume control appears to be fully electronic, in that the volume knob does not move when using the remote (unlike equipment that actually turns the not via a small motor).

Since this knob controls the gain on six channels, I would certainly not expect there to be 6 ganged pots or precision steppers hanging off the back of the knob. However, I would expect there to be some means to apply level control to all channels based on this one knob (duhhh).

Perhaps I would further expose my ignorance be referring to it as a digitally controlled analog level control? That would seem more logical, at least in my mind.

Still curious on just what is out there in the realm of affordable gear.

BGL

#6 of 7 OFFLINE   Martin Rendall

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Posted July 14 2003 - 04:53 AM

Brian,

Thanks for the noodling. A digital volume control would cost dollars to make... very cheap to produce. I would suggest, much cheaper than an ganged analog pot of any quality. Very easy to do multichannel that stays in step. Very easy to do trims for each channel. How much analog circuitry do you suppose it would take to have global trims, plus trims for different inputs... a feature offered by many receivers and separates.

I do remember seeing an old prologic gear (1992?) on which the remote volume control turned a master volume knob on the front of the receiver. That may have been analog.

Looking at the Bryston SP1.7 feature set, they boast a full analog path with analog volume controls for 2 channel. The omission of 6 channel seems suspect, to me. From their web site:

Quote:
While the SP 1.7 is a great multi-channel controller, there are those who still like their stereo in the analog realm; so, at the touch of a button, the digital circuitry can be bypassed and SP 1.7 operated as a Bryston audiophile-quality analog pre-amp. The bypass mode provides a totally discrete analog signal path — including an analog volume control. The signal does not go through any IC’s or digital circuitry from input to output.

Maybe I should post a thread on The Receivers/Separates forum just asking about how volume controls are done. I suspect this was the wrong forum for this topic. Or perhaps an moderator would like to move this thread?

Thanks,
Martin.
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#7 of 7 OFFLINE   Brian L

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Posted July 14 2003 - 05:19 AM

Quote:
Maybe I should post a thread on The Receivers/Separates forum just asking about how volume controls are done. I suspect this was the wrong forum for this topic. Or perhaps an moderator would like to move this thread?


This topic is not really fish, and its not really fowel, I suppose.

Would be good to hear from guys like John Kotches, who would have a better read on the actual circuit designs.

BGL





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