Take a look at the Motorola Part number MC14097B Dual 8 channel Analog Multiplexer / Demultiplexer. (CMOS logic guide DL131) You can Cascade them to add as many channels as necessary. (watch for fast rise times with that many channels running at that high of a frequency) These parts will run digital as easy as analog, just make sure the data is valid during the sample time for each channel. You could even run an intercom through it. Think of each channel as one circuit, run compression, then multiplex. Reverse at the other end. Gordon Varney ----- Original Message ----- From: Michael Rigby-Jones To: Sent: Tuesday, June 29, 1999 8:56 AM Subject: Re: digital audio again (less vague) > 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.