Last time I looked CD quality was 44.1 kHz.

44100 * 16 * 64 = 45.2 MBits/second.  Standard ethernet only goes to
10Mbits/second, although the newer standard is 100 MBits.

Of course you could use compression to cut down the bandwidth.  MP3 gives
pretty good results at only 128kBits/second.  To be honest if this is run of
the mill public address sounds then you could probably get away with a MUCH
lower bandwidth.  I've never heard in-store music that could be described as
hi-fi. I always thought they used a couple of old baked bean tins and a
piece of string :o)

Without wishing to be involved in politics, 17K is a pretty crappy wage if
you are expected to work with this kind of thing.  Especially with those
hours.

> -----Original Message-----
> From: Adam Davis [SMTP:adavis@BALADYNE.COM]
> Sent: Tuesday, June 29, 1999 2:33 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: digital audio again (less vague)
>
> Well, maybe I'm babbling here, but let's go ahead and design our own
> system for
> the thrill of it...
>
> Assuming you want cd quality stereo sound and 32 channels running
> simultaneously
> on one twisted pair, then you need:
>
> 14400 samples per second, 16 bits per sample, and 64 channels (32 stereo
> channels).  So you need to be able to move 14,745,600 bits of data through
> the
> cable.  Now, it is audio, and you really don't need to have it exact, so
> let's
> say that about 100 times a second you send a break which lasts for one
> chunk(16
> bits) which will give you only 14300 samples per second, but won't be
> audibly
> noticable.  Then you'll be able to synchronize the receivers.  Add the
> overhead
> of a start bit and a stop bit (for every 16 bits), and you end up needing
> to
> send 16.6Mbps through a twisted pair.  All you need on the receiver end is
> a
> chip which counts chunks (can't call it a byte, it's a 16 bit chunk) and
> puts
> every 32nd chunk on alternating ADCs.
>
> I haven't read up on rs-485 recently, but I doubt you'll be able to
> reliably use
> a run of the mill rs-485 transceiver for it.  You may even want to look at
> an
> ethernet driver.  At any rate, this entire system depends on a constant
> supply
> of data from the transmitter at a constant speed.  No need to deal with
> 'assembling' packets of data or buffering anything.  It's more of a
> multiplexing
> system than anything.
>
> -Adam
>
> John Perkinton wrote:
> > For some reason, even though the audio quality is unsurpassable through
> the
> > existing system, my boss wants me to design a digital audio version.
> This is
> > going to be a nightmare, he wants 32 stereo channels, down one pair of
> > cables. Everyone says its impossible including a few of my friends who
> work
> > for Philips, but cable TV does it using Nicam so why can't I.
> >
> > Any ideas, or should I just look for another job, as I only get paid
> #17,000
> > a year, and end up working about 75 hours a week with little or no
> holidays,
> > no paid overtime. If you have any ideas please don't hesitate to contact
> me.
> >
> > Please also let me know of any projects you have done, and I'll let you
> know
> > some other mad things I've done with PIC's.
> >
> > John Perkinton.