Date: Thu, 14 Aug 1997 23:10:45 -0800 From: Bobby Stewart To: Multiple recipients of list CHIPDIR-L Subject: RE: What is CMI? Regarding the question of the "CMI 8330 Audio Host VX" as relates to its capacity to communicate via the S/PDIF protocol. S/PDIF is an anacronym for the words: "Sony/Phillips Digital Interface" where IF is a commonly used anacronym for interface (sometimes also I/F). In the early days of digital audio Sony (being "THE" formative pioneer) developed a serial communications protocol whereby their machines could transmit audio data between each other. This protocol, named Sony Digital Interface (SDIF), consisted of separate audio data connections (two for stereo and 24 for their digital multitrack machine at the time) and a clock connection (generally running at 48 kHz for professional purposes or at 44.1 kHz for consumer) for synchronizing the receiving machine (slave) to the source machine (master). As Sony and Phillips collaborated to develop the standard for digital audio storage and distribution now known to all as the Compact Disc (CD) the need arose for a data transmission standard which would be less cumbersome (i.e. easier for typically dense consumers to connect without blowing something up). They borrowed the concept for serially transmitted data from SDIF and developed it into a standard which multiplexed (combined) the data from both audio channels of a stereo pair and added some control bits into the chain to be able to trigger functions at the receiving end such as copy inhibit or de-emphasis equalization. The resultant protocol, S/PDIF is transmitted on an impedance matched coax connection (75 ohms, I believe), usually connected with RCA type plugs (you know... some people call them phono plugs), especially for consumer applications of which there weren't many, where professional interfacing is usually with BNC connectors. Considering the signal degradation that can happen due to noise induction and other factors, and that sometimes machines were located considerable distances apart, professional audio applications required something more robust. The premier authority for the worldwide professional audio community, the Audio Engineering Society (AES), and the European Broadcasting Union (EBU) combined efforts to produce a suitable standard which was then called AES/EBU (go figure!!). AES/EBU digital audio serial transmission protocol is essentially the same as S/PDIF in construction except that the control bits take on different meanings and the transmission method is changed. AES/EBU was originally developed using 110 ohm impedance matched twisted pair cable utilizing 3 pin XLR connectors. As of late, however, things have shifted back. The AES has issued a revised standard allowing for transmission via (you guessed it) 75 ohm coax cable. I believe this has more to do with the application of digital audio in the video world than with almost anything else, and we know how video guys (no offense) like their coax. Interestingly, in between all this, many other standards have developed for the transmission of digital audio; most of them driven by the design of the manufacturers of certain pieces of digital audio equipment rather than any commonly derived standards body. One of the direct descendants coming of the AES/EBU standard and developed in conjunction with the AES is the Multi-channel Digital Audio Interface (MADI) standard. This standard, whose largest proponent at the time seemed to be Studer (a highly respected pro audio manufacturer specializing in tape machines, including 48 track digital machines), would provide the capacity for up to 64 channels of serial audio data transmission via one cable (usually 75 ohm coax or fiber optic cable). There is much more to tell, and I'm sure I've bored you already. I hope this provides some useful insight into the history of digital audio. For further information, check with your local electronics/book outlet or visit Mix Magazine's Bookshelf web site for "Introduction To Digital Audio" by John Watkinson at http://www.gibson.com/cgi-bin/mall/web_store/web_store.cgi?store=mix. My apologies for any misstatements I may have made, none were intended. Best regards, Bobby Stewart Stewart Electronic Services Servicing the Professional Audio Community Date: Thu, 18 Dec 1997 13:52:24 -0500 From: Jean-Francois Larin To: Multiple recipients of list EDESIGN Subject: Searching for a chip HT1869V Hi! I just bought a very nice sound card for my PC... Well, nice in some way, and not nice in other ways. It's a SoundPro HT1869V+ made by PCChips. When you disable the noisy power amplifier, the sound becomes allright and after a few twikkle with the configuration, you can make it work (with windows Nt 4.0 at least). It's a CHEAP card (23$ TTC), that comes with NO manual. In fact, there is a 3.5 diskette with a paper around it. The disk is the installation for win 95/dos. All this is not interesting for anybody here, I guess. The interesting this is that on the box, it's mentionned that it supports the SPDIF input output, and yes in fact there is 2 two-pins connectors on the card. SPDIF is a 'standart' format for digital interface between elements of a stereo system. It's used, for example, on Digital Audio Tapes, some CD player and Minidisc recorder/player. It sends a stream of bits, on a RCA or on optic-fiber. My problem is this: I want to hook my card on a Sony Minidisc player and which has only a fiber-optic interface! Anybody has experience in building a SPDIF RCA-Fiber converter? The most interesting is this: The pin on the connector is directly connnected to the main chip of the card which is a SoundPro HT1869V. With the spec sheet of the chip, I could figure out the spec of the SPDIF connectors. I wonder if anybody know a good searching engine for chips part numbers? Thank you. ************************************************************ Jean-Francois Larin Head Office: Software design 1025 St. Regis Blvd. Network Products Group Dorval, Quebec, Canada Matrox Electronic Systems H9P 2T4 Tel:(514)-685-7230 ext. 2041 Fax:(514)-969-6272 ************************************************************ Date: Thu, 18 Dec 1997 21:36:36 +0200 From: Kalle Pihlajasaari To: Multiple recipients of list EDESIGN Subject: Re: Searching for a chip HT1869V Hi, Elector Electronics Magazine has had a number of digital audio projects. They inevitably support both fibre and co-ax data and the connections are rather simple. Look up TORX173 and TOTX173 Optical devices, Toshiba makes them I think. The December 1997 issue has a Digital input selector project that has the circuit details laid out for you pretty clearly and allows you to use either type of input or output. The S/PDIF looks like a 750 mV p-p digital signal sourced and terminated with 100 Ohms. Capacitor coupled (100 nF) to a suitable threshhold detector. I think the bitrate is 2 Mbps and the baud is 4 Mbaud. The output on your card may be low power logic, buffer and feed into a TOTX173 as per application note :-) Cheers -- Kalle Pihlajasaari http://www.ip.co.za/ip Interface Products P O Box 15775, DOORNFONTEIN, 2028, South Africa + 27 (11) 402-7750 Fax: 402-7751 http://www.ip.co.za/people/kalle DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer