Re: Enable system volume when driver doesn't
Re: Enable system volume when driver doesn't
- Subject: Re: Enable system volume when driver doesn't
- From: Brian Willoughby <email@hidden>
- Date: Sat, 15 Mar 2008 00:00:55 -0700
This topic has drifted away from CoreAudio, but I still think it is
important to examine real-world uses for CoreAudio: what is
appropriate, and what is not appropriate.
It's great that Apple provides cool features like Front Row, and I'm
sure they want to make this work as widely as possible. But do not
confuse this with professional quality. If you are concerned about
the negligible shortcomings of D/A and A/D chains, then you need to
also be concerned about the shortcomings of digital volume. Just
because you hear about all-digital studios does not mean that they're
using digital volume the same way you want to, and if they are,
they're suffering from the very shortcoming that engineers here are
describing. I do not agree with you that Apple is missing out on
something here. Read on for specific responses...
On Mar 12, 2008, at 10:18, Mikael Hakman wrote:
On March 12, 2008 1:37 AM, Jeff Moore wrote:
On Mar 11, 2008, at 4:58 PM, Mikael Hakman wrote:
Yeah, but digital volume control will do things like magnify
the noise floor and other signal destroying effects (at least
form a mastering point of view). This is especially important
for input signals. So, no I wouldn't agree with you that the
digital computer business means we need a digital volume
control. It just isn't apropos for lots of apps.
First of all, in a DAW (remember what D stands for?) you have to
use digital level adjustment. There is no other way.
But you forget that the processing done by the DAW is pre-mastering.
After a piece of music has been mastered, you do NOT want to alter
it's volume digitally. Unless you do not care about quality at all.
If you do alter the volume of a finished audio piece, it should only
be done in the analog realm. As an example of the ultimate quality
experience, the best movies are mastered in THX, and the playback
system is calibrated to a reference playback volume. In other words,
you should not alter the volume at all for those entertainment setups.
Second, as I described previously, the only alternative in my
project (and in all digital-through paths) is inserting a D/A-
volume control-A/D sub chain in the middle. However good that sub
chain may be, it won't be better than the naked wire that would be
used otherwise.
This is only true if you're using powered monitors with digital
inputs, which are not as ideal as having separate power amps with a
good analog preamp. What you really need is a remote-controlled
analog volume on a surround preamp, then stay analog from there to
the amps and speakers. No need for digital volume anywhere, at least
not on mastered audio. If you build the system wrong from the start,
then you might convince yourself that you need a fix where one is not
truly necessary.
Are you trying to build a system that is both a studio for
professionals to create audio productions as well as a listening room
for non-professionals to enjoy finished media presentations? If so,
I think you have severely conflicted requirements.
Yes, by digitally attenuating the volume you decrease dynamic range
and increase quantization distortion. But let's analyze what
happens if you use that analogue sub chain as compared to digital.
Say that you want to attenuate 8 bits (-48 dB). Using 24 bits audio
you have left 144 - 48 = 96 dB dynamic range after digital
attenuation. If you use analogue volume control you will take your
144 dB (= FS), attenuate it by 256 and then you will do the A/D on
the attenuated signal which will give you the same 96 dB range
because the analogue signal input to A/D is now 256 times lower
than FS. In both cases you lose the same due to attenuation, but in
the analogue case you also loose due to D/A and A/D conversion, and
maybe also due to analogue imperfections (no analogue circuit is
perfectly linear). Therefore I cannot agree on that analogue religion.
You've only proven that you should not be doing a D/A and A/D chain.
With a proper audiophile surround system, the volume attenuation will
only happen at the master analog control, with no more digital
conversions subsequent to that. In the proper case, existing
quantization noise is lowered with the desired content, thus
maintaining the signal-to-noise ratio.
I've spent time in a lot of studios over the years. Many of which
have examples of the gear you list. I have never heard any of the
engineers wish for a digital volume control. They just reach over
to their console and turn down the monitor volumes (in the, yes,
analog domain). In fact, that's exactly what I do in my own studio.
Nonsense! Modern recoding and broadcasting studios are digital
through including consoles, mixers, everything. Smaller studios are
still partly analogue.
The examples you give are either people who are working with
unmastered audio, and/or people who have analog master volume
controls. Every studio ends with analog, even in an all-digital
studio, unless nobody is listening. Modern studios are not designed
for non-professionals to operate, so your requirement that this be
easy is contradictory.
There is a trend towards powered monitors with digital inputs, but I
do not believe this is audiophile quality in the best situations.
Just because it is all digital does not mean it is better. Any
studio with digital monitors is going to be inferior in quality
unless they have analog attenuators in the speakers which are
controlled from a central location (and I believe there are some
designs which do this, and you should investigate them - see Meridian).
From your answer I understand that I didn't manage to explain why
do we need functional OS X master volume control. It is _not_
the slider control, nobody here cares about that. It is the
remote IR control that the system volume control reacts to.
It's all the same thing really.
It's not the same thing. Run Front Row, then press + on remote
while on menu - it moves you to next item on the menu. Start
playing a track. Press + now - it increases the volume if you are
using an audio interface that enables OS X master volume control.
There are analog surround preamps with remote volume control. This
seems like what you need.
One other thing: what you are proposing _will_ bleed performance
from the system. You are talking about adding non-trivial signal
processing which means adding more buffers (and therefore memory
pressure) to the system in addition to the extra CPU time you'll
spend doing the work. For example, doing fully dezippered
software volume for a 32x32 channel interface is some serious
math. It will have the net effect of reducing the overall track
count that a DAW app can achieve which is probably the last
thing a studio rat is going to want to have happen. And the
extra memory usage just takes away from what the DAW app can use
for it's own purposes.
First of all I don't need 32x32 channels. I need 8 channels out.
I'm not saying that this master control should be always on or even
on by default when using pro-gear. But it should be possible to
turn it on at user's or programmer's discretion. Then I think that
the problems that these vendors have, and to a certain degree even
your company, is that you all se DAW as the only interesting audio
application/market. While DAW is very interesting for a number of
reasons, including technological and musical, it is only a very
small part of possible audio application uses. Turn your attention
to monitoring (in general sense), playback, broadcast, and
entertainment and you discover a huge market, at least as compared
to DAW.
You're in a strange middle ground. You want professional performance
without a professional operator, and that's just not very likely.
There is a wide gap between production studios and consumers, and
there is a wide gap between computers and home theater surround. You
may have to wait quite a while before these meet up.
There are very good engineering reasons why the better audio
interfaces do not have master volume controls. What I find lacking
are that the home theater surround processors do not have better
support for computer interfacing. Given your requirements, you'd be
better off with home theater gear, but you'll have to wait with the
rest of us while the industry catches up to the technology and makes
it easy to hook up and use.
Brian Willoughby
Sound Consulting
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