In article 4a6993d7.25650265@localhost, Don Pearce
wrote:
On Mon, 20 Jul 2009 16:41:41 +0100, Jim Lesurf
wrote:

Your warnings about the distortion in the headphone output, but I'm
guessing that most people will use the line output, which I presume
is clean.

I don't know. But my experience makes me reluctant to presume line
output will be clean. So I'd say "maybe" to that.


Well, my card (which is on the decent side of medium) is an M-Audio
24/96, and seems perfectly happy flat out.

That may well be the usual situation. But I have no data so can't be sure.

When I listened with a pair of headphones the sound was very loud
unless you wound down the volume a lot. So the gain applied between the
internal DAC and the headphone output stage was needlessly high. Would
have been fine if this had been reduced so 0dB didn't clip. So it all
seemed like careless design to me. The usual idiotic motto: "louder is
better".


None of that surprises me. Think of it like the volume control on any
amplifier. You don't expect the output to be just clipping from rated
input when the volume control is at max. If it did, most music would be
incapable of driving the amp to clipping. There is always some slack,
and your laptop's headphone socket shows that.

The distinction is that in this case the same 'volume control' adjusts both
the analog and digital outputs. And if you set the gain to '0dB' to be able
to obtain bit-perfect LPCM digital output with no conversions then the
headphone output will clip. Turn down the volume to avoid clipping the
headphones, and you can't get 0dB output from the digital output, and all
the values are scaled down needlessly

That seems crazy to me.


FWIW if I can blag a borrow I will try out some other USB 'soundcards'
to see how they work (if at all!) with Linux. Then report on what I
find out. A number of these have appeared recently. But I've only seen
limited results based on windows and macs.


Can you even get drivers for most of them? I use Asio here- I suppose
that is implemented in Linux as well?

Pass. Drivers can be a problem. Fortunately, a number of people who use
Linus spend time trying to reverse-engineer the details that some makers
won't release.

There are lists of devices for which drivers are available. The snag is as
I have mentioned, though. e.g. 'It works' does not guarantee that the sound
device can output bit perfect at the correct sample rate. Just that 'you
can hear something'. But then you can probably say this for various
hardware under windows as well. The industry seems to assume few buyers
will notice or care and 'canna be bothered' I guess.

Personally, I think it should be a legal obligation for makers to either
provide drivers or the info needed to write them. Refusing to do so is an
anti-competitive practice in my view. As such I suspect it may be illegal
in the EU, and probably also in the USA. If not, then it should be IMHO.

But my impression is that most devices that are popular soon have someone
manage to write a driver.

FWIW Canonical (the people promoting Ubuntu) are keen on ensuring things
like drivers appear as they want Unbuntu Linux to be a choice that most
non-geeks can be happy to use. The current situation means that drivers for
audio and video are more important than in past decades, as is a decent GUI
for those who are deterred by terminals and arkane commands. My impression
is that they have made progress in these areas. But there are still
problems with some makers and devices.

FWIW Cambridge Audio had already checked, and were able to tell me their
DACmagic worked OK with Ubuntu before I tried one. It uses a standard USB
'headphone' chip for receiving audio via USB. I suspect other 'audiophile'
units do as it is the easiest way for companies with no computing
background to get into the game. I will find out if I can experiment in
future. But given the availability of the DACMagic if I need another I'd
happily choose one if nothing else I preferred looked like working. Direct
any cash to makers who ensure their equipment does the required task! :-)

Slainte,

Jim

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