So you guys are still here???
Originally Posted by arnyk
I'll play the "Derivative Technology" card against that one. ;-)
I saw my first 16 bit 44 KHz capable ADC/DAC in 1971 and the application had nothing at all to do with audio. It also cost about a half million dollars so I knew for sure it was never going to be used for audio. BTW it was acutally capable of a true 16 bits and 200 KHz sampling and had analog multiplexors in and out. It was attached to this:
snuck in one night and did use it to digitize a LP... ;-)
Someone did? Hmmm. This technology is before my time
. Your comments that it was able to digitize audio with such high resolution and the ADC/DAC cost half a million dollars got my antenna up
. So I did some research. This is what I found.
The picture is that of Electronic Association Inc (EAI)'s 680. This was a hybrid computer that was analog but had a set of analog to digital and digital to analog converters that would let it interface with a separate digital computer. I assume this is the interface you are talking about. The interface was called the EAI 693 Hybrid Linkage Interface. I found a CMU 1971 document that was offering the 680 and 693 for sale. In there, they provided the original costs for each. The analog computer was $161,000 and the Linkage interface was $81,000. In the above you say that the cost of the ADC/DAC was $500,000. Even I throw the cost of the analog computer in there, we are at half the dollar amount you state. So that math doesn't add up, especially if one considers the cost of the ADC/DAC module along.
You next say that it was capable of 16 bits and 200 Khz sampling. That is remarkable resolution for its time. I researched this further and found a couple of university papers that had built FORTRAN libraries to access the 680/693 combo. One reference there set a limit of 30 Khz for the ADC the other said this:"the A/D conversion system consists of a fifteen channel multiplexer and a single high-speed analog-to-digital converter. The settling time of the multiplexer is 10 usec. The ADC converts signals between +- 10 volts to 13 bits (plus sign bit) resolution; conversion time is 20 usec."
So clearly this was not a 16 bit converter. 13 is a far cry from 16. 20 usec conversion times translates to 50 Khz. Adding the MUX time of 10 usec, we get down to 33 Khz -- pretty close to the other reference (not sure if the MUX had to be programmed every time or not). Either way a far cry from 200 Khz that you state in your post.
Then there is the issue of voltages and feasibility of hooking up a turntable to this system. You would have to build a level translator to drive an ADC that wants +- 10 volts. Hard to imagine you building such a thing just for this overnight adventure
. Then there is a matter of getting access to a computer system of this cost and screwing around with it. Even if you had, this is not a stand-alone ADC. It simply generates data that must be captured by the digital system. You would have had to write a program to capture that data. But where would you have put it? I am sure no one was giving you permanent storage to put the bits there for the data rates you are talking about. The "Winchester" IBM hard disk of 30 megabytes was not to be invented until a few years later after your experiment.
And what would you have done if you did record the digital samples anyway? The DAC would not have had the proper anti-aliasing filter if your 200 Khz spec is right.
Maybe you say that this was some other ADC/DAC. So I went searching for evidence of people having such capabilities. This is the reference I found on AES web site: http://www.aes.org/aeshc/docs/recording.technology.history/digital.html"1976 - The first 16-bit digital recording in the US was made at the Santa Fe Opera on a handmade Soundstream digital tape recorder developed by Dr. Thomas G. Stockham."
So what you are saying is that this bit of history on AES web site is wrong and that you had done this five years earlier in 1971. Quite amazing if true.
So.... how do you reconcile this data with your recollection? Is it possible you were mistaken about most of this? It is a long time ago so it would be understandable if so.