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: Brian Willoughby <email@hidden>
- Date: Mon, 21 Jan 2008 17:59:38 -0800
What is the FireWire interface with 32-bit integer format for digital
audio (SPDIF)? Does it need a special driver to work with a Mac?
P.S. DTS only uses the lower 14 bits of the audio sample, so that
the digital noise is at -12 dB. Seems like a shame to lose 96 kbps
of bandwidth.
Brian Willoughby
Sound Consulting
On Jan 21, 2008, at 13:59, Mikael Hakman wrote:
SPDIF and its professional counterpart AES define other useful
streams besides the audio data stream. Having all bits served would
allow for using these low-bandwidth information streams. Furthermore,
AES standard requires a digital device to either mute or correctly
process compressed bitstreams. This is so that you don't mistakenly
get un-decoded DD or DTS reproduced, which at 110 dB is worse than an
earthquake, at least sonically. I did it once when evaluating active
digital studio monitors and I don't want to experience that once
more. Not many professional equipment vendors implement compliant
behavior because of the difficulties in doing so. Having easy access
to the flags would make such compliant implementations more frequent.
The other device, an FW interface, in about the same price segment
does this well, at least according to the spec. When requested, the
device passes all the extra bits and flags in the 4th byte of your
audio sample (least significant byte) provided that you also request
a 32 bit integer format - even if you don't do anything special, that
byte is far below audibility limit. I intend to evaluate this
equipment very soon.
Regards/Mikael
Brian Willoughby <email@hidden> wrote:
For the longest time I have wanted an SPDIF interface for the Mac
(FireWire?) which allows access to the full 32-bit word. Problem
is that the Crystal part interprets the bits and delivers audio
sample bits (up to 24) on a separate pin from the control bits (up
to 16). This is handy if you don't have a processor available,
but it limits what can be done if you do. It would certainly be
possible to just give the Mac a 32-bit stream and let the Mac
split that into audio and control, but it would require custom
silicon - unless there is already such a chip and I've missed it.
Flags and block starts would be a cinch this way.
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