Serge Auckland wrote

The DSP solution would appear to be preferable. However, presumably there are
rounding errors. That is, if I divide every word by a constant, each result
must be rounded to the nearest step, and this rounding error is not linear
wrt the audio signal. I assume there is a name for this kind of error? How
significant is it?

The DSP solutions I'm familiar with operate either floating point or 32 or 48
bit internal which means that when the output is finally reduced to 16 or 24
bit the errors from the DSP calculations are minimised.

The error would be reduced by the same ratio as the conversion I suppose.

I don't know of a specific name for the errors resulting from DSP operation.

Perhaps it is no different from the usual sampling error, and possibly makes sod
all difference to the total.

A digitally controlled attenuator chip contains not only a resistor ladder,
but also a heap of semiconductors to do the switching. I expect those who
object to them are wary of the SS junctions in, and perhaps also parallel to,
the signal path.

A motorised pot may be an expensive component, but it is easier to program
the control system. The pot remembers where it is, and only needs 2 bits to
control. OTOH, it is not convenient to use if you want a rotary control on
your remote.

The main problems with all pots, motorised or otherwise is tracking over a
stereo pair.

Yes, good point. I guess better matching is part of why better quality stereo
pots are better, but the problem is always there to some extent. I get the
impression these days that the best digital attenuator chips are at least as
good as anything else.

With 5.1 surround, there would have to be 6 tracking controls so some form of
electronic volume is almost essential.

I guess so...and much more than 6 times harder to match. Not into multichannel;
it's bad enough having to make everything twice.

I have never seen a remote with a rotary volume control. Why not? If the link
is reasonably error free, then it should be possible to put a rotary encoder
on the remote as well as on the system case. I hate push-button volume
controls.


I don't think I've ever seen one either. The closest was a rotary shuttle
control for a S-VHS VTR which would allow frame by frame forward or backwards
movement. Now that I think about it a bit more, didn't QUAD have one on their
66 and 77 series?

Looks like it in this pic

http://www.whats-new-at-totallywired.com/specials.html

Come to think of it, not easy to do with the usual remote coding systems. The
most reliable way would be to send the absolute position, rather than a string
of increments. That would require a different code for each position of the
attenuator. I guess Quad used their own coding scheme. DIY remotes tend to use
RC5 or Sony codes, so you don't need to make your own transmitter.

I have a remote output level control on this quirky Sony CD player that I can
compare quite easily with my Alps pot. I have never tried it because it defaults
to bypass on power-up. I'll give it a try and report back if I can hear any
difference. Don't wait up...

Oddly, and infuriatingly, this same machine uses a front panel pot for the
headphone output, with no control on the remote, AFAIK. I wonder how they make
these decisions.

cheers, Ian