why does digital volume control cause loss in info

Shadorne: Thanks. Not sure, though, that it's fair to say that properly applied dither will necessarily make a digital volume control "as good as analog." It will certainly reduce the subjective objectionability of quantization noise. But I suspect that it could not adequately compensate for the loss of say 4 or 5 bits, corresponding to a volume control setting that is 24 or 30 db below maximum.

You have to consider that most home audio systems have a dynamic range of only about 60 to 70 db to begin with.

Think about a typical noise floor of around 30 db SPL and then a typical max undistorted SPL of 100 db SPL (played at maximum volume)

So, with this perspective, either digital or analog volume of a 96 db dynamic range CD is more than good enough. Most systems can't even exploit a well recorded CD anyway.

When you get into pro equipment with 120 db SPL continuous output at less than 0.3 THD over the entire frequency range then you can begin to benefit from 24 bit technology (in an audible sense when playing back music)

So from my perspective the benefits of analog over well implemented digital volume control become theoretical in most cases (as you cannot actually hear it in a real room although you might measure it with an oscilloscope)

So from my perspective the benefits of analog over well implemented digital volume control become theoretical in most cases (as you cannot actually hear it in a real room although you might measure it with an oscilloscope)
Shadorne

Shadorne, Wow! That statement blew me away.
On a forum where members argue that 3 feet of special power cord can make a huge sonic difference, measurements be damned. That statement surely constitutes blasphemy. I applaud you!

Almarg...I know about this chip because one failed in my MAP1 and was replaced (on waranty). Sorry I can't cite the exact part number. There are three of these 2-channel chips in the six channel preamp, so they can't cost that much.

Eldartford,

You are probably thinking of the Crystal CS3310 chip it is common in many devices.

I took a quick look through the CS3310 datasheet. It looks like a pretty nice device, although I'd expect that designing with it, and achieving good results, would be a non-trivial challenge because of the presence of both digital and analog signals and power on the same device. And I note that its datasheet was initially released in 1991, so there may be newer and better comparable devices available now.

Digikey charges $6.57 for it in quantities of 1000. I believe that a generally accepted rough rule of thumb for equating parts cost with final assembly selling price is to apply a factor of 5. So it would have about a $33 impact on the selling price of an audio component, or perhaps say $50 to $100 factoring in possible requirements for additional surrounding circuitry to interface to it, and additional circuit board real estate that may be required. Not a huge cost, but certainly significant.

A purely digital volume control, on the other hand, could perhaps be implemented within a custom digital chip that is required in the design for other purposes, resulting in negligible impact on recurring cost.

Thanks for pointing out this device, ElDartford and Shadorne.

Regards,
-- Al