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Re: Audio interfaces survey
one issue to consider is how many channels you need and what sampling
rate you want to use, as well as how much external circuitry (like
preamplification and antialiasing filters) you will need.
For multiple channels general DAQ cards can be a good choice. I'm
currently using 4 National Instrument PCI-6071E cards, all together in a
computer and I'm acquiring from 128 channels at 39.0625 Ksamples/sec
each. This cards do require external preamps and unfortunately NI does
not offer any solution for this high channel count that could make sense
from the size/price point of view.
Regarding the sampling rate, multi channel cards usually divide their
max sampling rate among the number of channels used.
Another issue to consider is leak between consecutive channels, which is
an issue if you have signals of very different sizes.
and ... one more issue ... if you need to synchronize input and output
accurately, on the same clock, you may want to consider a card that has
also D/A. The above cards have 2 of these channels each which you can
trigger with a hardware trigger (and independently from A/D if you want).
Hope this information helps.
Regis Rossi A. Faria wrote:
sound cards generally target PC/Mac buses, like PCI or USB or Firewire:
this is an issue: connectivity! Firewire is apparently more stable than
USB for audio applications specially regarding high bitrates transfer
sustain, and PCI bus is the one which offers lower latencies. Terratec,
Yamaha, Creative and many others target this market.
digital audio interfaces target not only computer buses, but also studio
gear which connectivity to analog mixers and analog/digital/analog
converters: RME, MOTU, Egosys, M-Audio, and many others target this
market. Usually they offer lots os possible digital formats/protocols
for I/O: ADAT, TDIF (both now decrasing popularity), Firewire and USB
(increasing popularity), PCI, SPDIF, AES/EBU, very few would support
MADI (AES10) and some are very focused in having multiple (usually 8)
D/A and A/D conversion are now stable in the range 96 kHz/20bit, most
cards accept simultaneous I/O of multiple channels in this format, and
lots of cards/interfaces offer now 192 kHz/24bits, although not
supporting many inputs or outputs operating at the same time in realtime.
You should pay attention to the pictures of the back and front panels,
where you will really realize how many inputs and outputs the interface
has, and then how many inputs and outputs you can connect phisically:
many manufacturers count on maximum possible digital channels supported
by the card, but these figures generally are not accessible in the real
conectors, or require that you have several different gear at the same
thime, for example an ADAT system, a SPDIF I/O, RCA line inputs and the
TRS/XLR I/Os. That's tricky.
Other issues regards to OS compatibility and support, THD and SNR
figures, dependency of a PC/Mac to operate or standalone, mobile or rack
mount, and support to additional formats (ex: MIDI).
Hope this helps,
Regis Rossi Faria
LSI-University of Sao Paulo
Olivier Tache escreveu:
I'm currently working on a very general survey of digital audio
interfaces, but i'm unfortunately lacking practical experience on the
subject. It would be very kind if those who are willing to could
briefly tell me about the typical issues they encounter when dealing
with sound cards (latency, D/A and A/D conversion, etc.) or provide
pointers to ressources that could help me in my *quest* (apart from
those wich have already been given here a few months ago).
Thanks a lot.
Elena Grassi, Ph.D.
Perceptual Interfaces and Reality Lab
University of Maryland
3355 A. V. Williams Bldg
College Park, MD 20742
301-405-2876 (office) 301-314-9920 (fax)