From: jboone@WTFD.ORST.EDU (Jared Boone)
Newsgroups: rec.audio.pro
Subject: Re: Interface Digital Audio <---> Computer ???
Summary: Long, boring, dissertation on IBM PC ISA bus speed.
Keywords: PC ISA BUS DIGITAL AUDIO RECORDING MULTITRACK
Date: 24 Nov 92 01:01:42 GMT
Article-I.D.: talon.1erutmINNfjr
Organization: Weatherford Hall, Oregon State University
NNTP-Posting-Host: wtfd.orst.edu

(For those not interested in technical mumbo-jumbo, my answers are at the
bottom of this article...)

I hope I'm not getting too far off the subject, but the IBM PC ISA
bus is quite capable of moving two tracks of 16-bit digital audio on and off
a hard disk.  The bandwidth requirement is:

	48,000 samples/sec x 2 bytes/sample x 2 channels = 192,000 bytes/sec

I borrowed a very good book about the ISA and E-ISA (not EISA) busses during 
the summer, and am trying to remember the best I can how many clocks are re-
quired for the several different types of data transfers...

	8-bit I/O address space access:		4 BCLKs (I think)
	16-bit I/O address space access:	3 BCLKs (I think)
	8-bit memory space access:		3 BCLKs (I think)
	16-bit memory space access:		2 BCLKs (I'm sure)
	DMA access (many varieties):		2-8 BCLKs (I think)

One BCLK is defined as the duration of one ISA bus CLOCK cycle (not BUS cycle)
and is typically 1/8.33MHz or 120nsec.  The best way to eke out all the avail-
able performance is to use a 16-bit memory transfer.  This fully utilizes the
width of the ISA bus, requires the least amount of cycles per access, and is 
free of recovery time limitations (unlike I/O accesses).  So, using a 16-bit
memory access, a theoretical transfer rate of:

	(8.33MHz cycle clock) / (2 cycles/access) x (2 bytes/access) =
							8,330,000 bytes/sec

...is possible.  This is plenty of bandwidth for two-track audio.  I'd say --
from a practical view -- that the ISA bus is realistically limited to sixteen-
track audio.  That amount of audio would require 1.5MB/sec coming to/from an
audio I/O board, and then, 1.5MB/sec of audio going to the hard-disk subsystem.
The drive controller would need to be a bus-mastering type (more speed) and the
audio I/O card would need some sizeable data caches that the drive controller
could directly read from the memory address space.  It'd also be good to get a
"real" operating system -- i.e. Windows NT -- to handle all this throughput in
a more refined, modern way (no sloooooow DOS/BIOS function calls).  But I di-
gress.

It's definitely possible to do two-track audio.  You can get the MediaVision
ProAudio Spectrum 16 card for about $220 which can record and play back near-
CD quality audio (44.1KHz, 16-bit stereo, but only 85dB SNR -- gee darn).  It
works quite well, but the software is a little non-existant.  Turtle Beach
makes the MultiSound card -- that has better A/D/A converters on it, and also
a Proteus and a Motorola DSP.  It's stereo and has far better software for ed-
iting digital audio.  It's more expensive of course -- $995 retail.  The true
professional cards for the IBM PC are:

	o Digital Audio Labs -- The CardD System -- $1045 to $1340
	o Turtle Beach Systems -- 56K Digital Recording System --
		$1495
	(these were listed in Electronic Musician, Sept. 1992)

The choices are limited, but they're all good systems (from the reviews I've
read).  Good luck...

							- Jared Boone
Newsgroups: rec.audio.pro