1. Home
  2. Electronics Design
  3. 1% 8 bit R2R DAC @ 44KHz = Joke?

1% 8 bit R2R DAC @ 44KHz = Joke?

I'm trying to make a stereo audio playback device with a frequency response up to 20khz. I am feeding 16 bits of digital PCM audio into a

16bit shift register which has a storage latch, and then latching the output into an 8-bit R2R DAC in 100ns. The R2R dac is discrete, i.e. a bunch of resistors tied together with a buffer opamp. I'm wondering how imprecision in the resistor values (they will be 1% tolerance) affects the output? I.e. if I looked at the FFT of the original and the FFT of the output, what differences would I see? (ignoring quantization effects)
Reply to
acannell
Loading thread data ...

Archie Bunker would have said "louseh". For audio eight bits ain't much to write home about. Imagine that the MSB resistor is 1% off. That's already about twice as much as the contribution of the LSB resistor.

You could measure them all out and put a correction LUT in. Or use precision resistors or better yet a "real" DAC.

Regards, Joerg

formatting link

Reply to
Joerg

Hi,

As long as you are shifting out your data anyway ... try a phillips TDA1312 16-bit stereo DAC.

Luhan

Reply to
Luhan

FWIW, you can get little SOT DACs from Analog Devices like AD5300, AD5301. They also have pin- and protocol-compatible 10 and 12 bit versions (probably higher, too, but I haven't looked at them).

--
Ben Jackson

http://www.ben.com/
Reply to
Ben Jackson

Back some 40 years ago, when 16-bit DAC's were horribly expensive, I demonstrated a system that had 8-bits of resolution plus 8-bits of "gain-riding".

It was for the (IIRC) L-1011 aircraft passenger audio system.

Sounded great!

They chose instead to pay thru the nose and went with 16-bit DAC's :-(

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Hello Jim,

Maybe the stuff I did was similar. 8-bit DAC, feedback and another 8-bit DAC of same breed as a "modulator". If that's the same you'd hold the title since I was still swinging from trees 40 years ago.

16-bit in a Lockheed? Somehow that doesn't seem to make much sense.

That is sad. Did they think you were too young?

Regards, Joerg

formatting link

Reply to
Joerg

Precisely (both sentences ;-)

That's what they wanted. I always liked the 1011... don't know why it faded away so quickly.

Probably, I was only 26 ;-)

Gawd! I feel old now!

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Hello Jim,

The Tristar is a great aircraft, huge. They didn't fade, LTU (the tourist branch of Lufthansa) used lots of them. I wouldn't be surprised if they still do. Once my wife and I had the pleasure to hop on a ferry ride from Dublin to Shannon. Just imagine, about 20 passengers in a

1011. "Take any seat you want" the stewardess from Air Caledonian said.

That's about how old I was when I did the DAC trick. Had to, because anything else was very expensive since this was RF stuff.

Nah, my great-grandpa hopped on a motorcycle at 95. He didn't understand our worries. "But I had to buy some new shoes".

Regards, Joerg

formatting link

Reply to
Joerg

I did one last year that was linear in dB's... at 500MHz.

I thought you were going to say "underwear" ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Wasn't that the one that they nicknamed "the swamp buggy", because they kept crashing in the Everglades or something?

Thanks, Rich

Reply to
Rich Grise

I was on a 747 ride like that once - about a half-dozen of us went upstairs to the lounge and sat on the floor and played cards. :-)

Cheers! Rich

Reply to
Rich Grise

Just the once--and it was stupid humans that caused it (the aircraft commander didn't delegate responsibilities properly). The airplane was only fractionally to blame. (I have never felt more safe flying than in a TriStar.) http://66.102.9.104/search?q=cache:DyIUMIPeXr8J:trijets.net/tristar/page/accident.html+Everglades+L-1011+light-bulb+autopilot+microburst+Dallas

The one that sticks in my mind is the burned-out ass end on the end of the runway at DFW. http://66.102.9.104/images?q=TriStar-N726DA-Dallas (The impetus for all the Doppler-shift radar we have now.)

Reply to
JeffM

If the resistors are from the same tape or reel changes are good that they match to 0.2% or even 0.1%. That would be suitable for a 10bit dac.

10bit audio can sound quite good provided you filter off the noise. 
--
Dipl.-Inform(FH) Peter Heitzer, peter.heitzer@rz.uni-regensburg.de
HTML mails will be forwarded to /dev/null.
Reply to
Peter Heitzer

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.