Re: NE570 or 571 Companders

[shalish]

REMINDER ----- Original Message ----- From: shalish To: [EMAIL PROTECTED] Sent: Friday, February 20, 2004 7:02 PM Subject: Re: NE570 or 571 Companders Sub : Marketing of your product services in INDIA.   Dear Sir/Madam,   We shall be pleased to forward your e-mail to  data base of 30,000 Indian opportunity seekers, Importers, Wholesalers,  direct buyers interested in your products and services through individual e-mail to each e-mail address from our Data Base.   To avail our services, please send USD100/- by Banker's cheque in favour of World Trade Connections- India drawn on U.S. Banks.   We await for your prompt response.   Sincerely yours   Shalishkumar World Trade Connections 2nd Floor, B-166, Shrenikpark Opp. Akota Stadium, Productivity Road, VADODARA-390 020 [GUJ.] INDIA Telefax: +91 265 2342148 e-mail: [EMAIL PROTECTED]     ----- Original Message ----- From: Martin McCormick To: Multiple recipients of list CHIPDIR-L Sent: Thursday, February 19, 2004 10:19 PM Subject: Re: NE570 or 571 Companders I must respond to some of this message. When I was in Graduate School in 1977, I did a report that Summer on synthetic speech systems.  I read a bunch of Bell Labs' "Benchmark Papers on Acoustics" and other interesting stuff and was going to try to actually build a device that could make speech sounds. My knowledge and the technology available at the time were not quite up to the task yet, so I ended up writing a report on how it is and had been done plus I built an analog to digital converter and a digital to analog converter that more or less worked. It was how they worked that, in retrospect, seems really dumb. What I did was to run a voltage controlled oscillator chip (MC4024)  in such a way as to allow audio to modulate the frequency of the oscillator which swept a range between 1.536 MHZ and twice that frequency.  I then built the beginnings of a frequency counter whose reset strobe operated at 6 KHZ.  256*6000 = 1.536 MHZ.  The counter was supposed to go through one complete cycle and be back to 0 for the low end of the range.  As the oscillator neared  3.072 MHZ, the counter which was a pair of 7493's would go through 2 cycles and at 3.072 MHZ was at 255 or 0XFF.  To get a digital sample, I strobed the clock line on a pair of 7475 latches.  It really does give you a 8-bit digital representation of the signal. In order to make that signal analog, I used weighted resistors, so that was the D/A converter. You could feed audio in to the VCO and what came out was pretty darn bad, but it was recognizable.  It would have been a lot better with low-pass filtering, but it did work as long as you didn't let the oscillator stray above or below its range. When it did, the results were catastrophic to say the least as the counter would overflow or underflow, causing a completely bogus reading. The successive-approximation-type A/D converters used today have it all over this scheme, but it is proof that there are many ways to skin a cat.  The audio taken from the common point of the weighted resistors sounded more like the cat being skinned alive since you could hear the 3 kilohertz sampling rate and all that aliasing, but my instructor took pity on me, I guess, and I passed that course.  I truly learned a lot that Summer.  At the time, I was planning to teech basic electronics in a vocational/technical school or junior college so the synthetic speech was more of a side issue in my studies, but it was pure fun. Martin McCormick WB5AGZ  Stillwater, OK OSU Information Technology Division Network Operations Group Declan Moriarty writes: >Here's one for the nuttier ideas ever expressed on this forum, but you >might love it :-). > > >A guy I know made just such an adjustable digital pot as follows back in >1979. He took his signal, ran it through an 8 bit a/d, inverted all >lines, and ran it out through a d/a. Adjustment was provided by tweaking >the reference voltage to the d/a. Whether the inversion is needed or >not for your application, I don't know. Slap a bit of smoothing (0.22uF) >on the output and you have audio quality. -- Author: Martin McCormick   INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from).  You may also send the HELP command for other information (like subscribing).