Re: high quality audio output
Re: high quality audio output
- Subject: Re: high quality audio output
- From: "Cor Jansen" <email@hidden>
- Date: Thu, 30 Nov 2006 14:32:28 +0100
Hello again
My DAC does reclocking, so I hope the clock will not be the main reason for
the difference.
It would be great to have a Toslink analyzer like Brian Willoughby is
suggesting, but quit a bit of work.
I was thinking of an output device for the macMini that is not sending the
samples to the SPDIF port, but to
a file. Or better, to both the file and port. Then I could check the file
data agains the original wav file.
Can this be done? Or does it exists already? I do not know enough about the
Apple audio architecture (yet).
Using the optical input may be the easiest way to go. I agree it is a little
dangerous to use the macMini to test itselfs.
But when the resulting file equals the original file, I think it is must
mean that the data on the optical wires is the same too.
Or not?
And Brian:
About the difference in AES/EBU versus S/P-DIF differences where you are
talking about, I'm a little
confused. Isn't S/P-DIF (almost) the same as AES/EBU?
Or do you mean copper when saying AES/EBU and optical when saying S/P-DIF?
I know that for the serial protocol the clock is recoverred by checking one
particular signal edge in the protocol.
Depending on the bandwith of the connection and medium, jitter will be added
because of the inter-symbol interferention.
For optical (lower bandwith) this will be worse. Maybe this can explain the
difference in your case?
Regards, Cor
[ Somehow when I play music using my miniMac and iTunes, it does not sound
the
[ same as when playing from my CD player.
[ Almost the same, but not exact the same.
[ In both cases I use an optical connection to the DAC and amplifier.
There is a very good reason why a DAC+amplifier could sound different when
fed
exactly the same data from two difference source devices: The accuracy of
the
clock on the S/P-DIF output can really make a difference.
I really hope the Mac mini sounds more correct. However, beware that
sometimes the human ear favors slight distortion and may prefer the less
accurate digital source. i.e. Don't always trust your ears, unless you've
trained them to distinguish different kinds of distortion.
[ So I was thinking I need to write my own audio unit.
[
[ How can I be sure the output is exactly the same? Is there a tool that
will
[ dump audio samples to a file?
I still doubt you need to write an AudioUnit. However, you may need to
write
some software before you're done.
If you are serious about this, then you should obtain some kind of digital
optical recording device that is bit accurate. You might be able to use
the
Mac mini digital input, but I guess there might be some concern about
using the
Mac mini to test itself. On a budget, I don't see any reason why that
wouldn't work, though. It will be difficult to compare the data between
your
CD player and iTunes, simply because you won't be able to line up the
recordings very easily, especially not the CD player which has no external
sync. You could author a CD with a click followed by some quality music,
and
then line up the click from each recording. You may need to write
software to
compare the two recordings, although I have used Logic Pro to do this by
using
the "invert" plugin that ships with Logic Pro and mixing both stereo
recordings
at equal levels. They should completely cancel out if you've lined them
up
precisely, and a good meter will tell you if there is any signal. Try
this out
with the same recording on two tracks to make sure you understand what
happens
when they do match, and then try it with your test recordings.
In my personal experience, feeding digital inputs from FireWire devices
via
AES/EBU sounds much better than from USB devices via S/P-DIF. But that's
just
with the specific brands of audio interfaces that I have in my test lab (2
different FW, 5 USB). It may or may not be directly related to the bus
technology. It's all about the quality of the clock signal. Of course, I
have
different cables on each, and the input switching network on my DAC might
not
treat AES/EBU inputs exactly the same as TOSLINK. However, the sound is
clearly different, even when playing from the same computer and switching
the
default output device between FW and USB.
P.S. Now you've got me curious. I just might set up a test to compare
FireWire to USB with both going over S/P-DIF, just to eliminate the
AES/EBU
variable. That's one combo I haven't tried, simply because the FireWire
device
is question is rather new. It will be interesting to see if there is as
much
of a difference.
Brian Willoughby
Sound Consulting
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