Re: I/O device with multiple *independent* SPDIF ports?
Re: I/O device with multiple *independent* SPDIF ports?
- Subject: Re: I/O device with multiple *independent* SPDIF ports?
- From: "Mikael Hakman" <email@hidden>
- Date: Mon, 21 Jan 2008 13:12:43 +0100
- Organization: Datakonsulten AB
Stephen Davis <email@hidden> wrote:
In an early iteration of the project, I *was* planning on making it a
mixer and allowing multiple inputs to be active simultaneously. In
reality, I only want one additional input to always be active and that
input is the Mac.
Anything coming from inside of Mac can be easily mixed with the "normal"
output. After all, inside is one (or 2 - 3) normal sources too - music,
video, CD/DVD audio/video for example. Also processed input will come from
"inside" because it is the inside that does the processing.
This is an interesting idea - to replace all these boxes with a computer.
Currently I'm using active digital speakers and digital LCD so theoretically
I shouldn't need anything else than a Mac with right interfaces and
software. It sounds simple to beginning with but you realize that it's more
complex after you analyze all the details. To make the whole thing working
smoothly and robust with user friendliness acceptable to average home and/or
professional (not necessarily computer-savvy) user can be difficult. AFAIK
nobody has achieved that yet. Currently, all those HTPC and HTMAC projects
are not at this level yet - too much to setup, adjust, optimize, and reboot
all the time - too much PC, too little HT, IMHO. For some time ago I started
such a project somewhere between hobby/home (for myself and friends) and
proof-of-concept commercial (for audiophiles and studio people). Maybe it's
time to activate it again.
(to allow voice notifications or other alerts always come through). In
that scenario, I can just use a virtual device a la the AudioReflector
driver or Soundflower for the "Mac input" side.
Currently I settled down on using smaller desktop USB speakers for system
sounds while media audio output is going to my main speakers. Why? Because
having system BOING or iChat calling you at 90 dB may cause heart attack.
AC/DC at this level is fine!
So, an external multi-port SPDIF switcher is in fact what I'm looking
for. Thanks for the good pointers, those sites look like they'll be a
lot of help. I have used the Crystal parts in the past but it looks like
there are some SPDIF switchers available already, now that I'm googling
on the right search terms.
Please keep me (us) updated should you find good quality inexpensive one.
Stability of device's clock is what matters for sound quality. Then of
course you want 6 (or 8) channels, up to 96 kHz (192 kHz better) and 24
bits/sample. Then the thing starts to cost some real money.
As for the auto-detecting of bitstream vs. PCM goes, I have that working
for DD but haven't looked into the audio/video sync issue very closely
yet. In cursory experiments, it seems to be fine. The DD bitstream lets
you decide pretty quickly what mode you're in but I'm sure it will take
some work to get the latency down low enough.
When I did my experiments, I had to buffer more than one whole SPDIF block
before knowing for sure whether it was PCM or DD or DTS. Then I needed a
whole block before I could decode it, and then there was decoding time, and
then there was some latency in OS and devices (both in and out). All this
together made an unacceptable delay between audio and video. This is when I
gave up. The problem is that the syncword used in DD and DTS is a valid PCM
value and that the DD/DTS flag in SPDIF is normally not available outside
the device, and not always set, and that you don't see in your code where
each SPDIF block starts - you only see a buffered continuous stream. Perhaps
you found a clever algorithm for this - could you share it with me, please?
Thanks/Mikael
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