AD Converter - Choosing, Testing

[Picksalot]

I was looking for some technical information about "AD Converter" and ran across an outstanding paper. It is excellent and written in a style that even non-engineers can understand. Technical terms and acronyms are explained within the text. Examples are given, as well as ways to test AD converters! The paper is actually enjoyable to read.

The paper is called "Measurement and Evaluation of Analog-to-Digital Converters Used in the Long-Term Preservation of Audio Recordings" by Ken C. Pohlmann, University of Miami, Frost School of Music. "This paper was written for the roundtable discussion, “Issues in Digital Audio Preservation Planning and Management,” held March 10-11, 2006, in Washington. D.C. The meeting was convened by the Library of Congress and Council on Library and Information Resources on behalf of the National Recording Preservation Board."

Wow, that was quite a mouthful, but please don't be put off. You will be amply rewarded by reading the paper which can be found here: http://www.clir.org/activities/detai...s-pohlmann.pdf.

Hope this helps those who have questions about AD Converters, Soundcards, etc.

If you're an Audio Engineer with lots of technical background and experience, please share your assessment on the accuracy of the paper. I'm sure others, like myself, that don't have the technical background to evaluate the accuracy of the article would be interested in what you have to say.

Even if you're not an Audio Engineer, please feel free to share your comment on the article and if you found it valuable to read.

Here is an excerpt from the article for your reading pleasure:
"An A/D converter is susceptible to jitter, defined as a variation in the time base of the clocking signal. Random-noise jitter can raise the noise floor and periodic jitter can create sidebands, thus raising distortion levels. Generally, the higher the specified dynamic range of the converter, the lower the jitter level required (Harris 1992). A simple way to test an A/D converter for jitter limitations is to input a 20-kHz, 0-dBFS (full-amplitude) sine tone, to observe an FFT of the output signal, and then to repeat the process with a 100-Hz sine tone. An elevated noise floor at 20 kHz compared with 100 Hz indicates a potential problem from random-noise jitter; discrete frequencies at 20 kHz indicate periodic jitter. Jitter is inherent in any digital device and it can never be eliminated. Highquality A/D converters contain internal clocks that are extremely stable, or when accepting external clocks, have clock-recovery circuitry to reject jitter disturbance. It is incorrect to assume that one converter using a low-jitter clock will necessarily perform better than another converter using a high-jitter clock; actual performance depends very much on converter design. Even when jitter causes no data error, it can cause sonic degradation. Its effect must be carefully assessed in measurements and listening tests."

[magno]

so let's see the jitter test so I cam sleep tonight/

[brandondrury]

I have a section in my upcoming recording book entitled "Getting Too Caught Up In The Science Side". It basically points out that for every physicist comfortable with splitting atoms and reading technical papers such as the one here, there is a stoned idiot in touch with the universe cranking out just as good of recordings even if he is oblivious to why things happen.

It certainly doesn't hurt to do the homework. In my early years I did gravitate towards the technical side as this was more in line with my instincts. However, over time I've grown to feel that I'm more interested in the things that can't be plotted on a graph (physchology may be the old science I'm really interesting in regard to music, I guess).

So enjoy this pdf. It explains the fundamental concepts. If you make better music because of it, great! However, just remember there is a self serving element to this that may not improve recordings in the slightest bit.

Note: One other thing. My Distressor came in today. My Distressor EL-8X....after 60 minutes I've been using Distortion #3 on it mostly. It has a harmonic distortion of .5-20%. The MINIMUM distortion is .5%. Just remember that when we compare converters with distortion ratings 1/1,000th of this.

Brandon

[Picksalot]

Brandon - Couldn't agree with you more. All the technology is there to serve the music, not the other way around.

I believe that audio technology surpassed most peoples' biology years ago. I posted the link to the paper so people could understand the terms, etc. and not be manipulated into thinking they were getting more for their money than promised. Knowledge is powerful.

Be informed and make wise decisions. Don't waste your time and money on promises of technology that could probably only be enjoyed by bats, dogs, dolphins, and a very few people on the planet.

Go forth and make the best music you can. The technology you already have is probably overkill. Talent, inspiration, and hard work make good music, not technology.