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)

 

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

 

Hi,

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

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).

 

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

 

Oh, shut up... That was just after WWI when people were converting Avro's
for trips to the seaside. America hadn't even been invented and you're
babbling on about how you designed the tampon!

DNA

 

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

 

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

 

If Al Gore invented the Internet, _I_ invented the tampon ;-)

...Jim Thompson

 

I don't see how A1 Gore and the internet are related. How do flat hedgehogs
come into this? I might see the tampon link but I wouldn't want one in mine.
Perhaps it's a cultural thing....

DNA

 

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

 

Did you use it?


martin

 

Yep. Shoved it up the ass of a leftist weenie ;-)

...Jim Thompson

 

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

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

...Jim Thompson

 

With or without the hedgehog?

DNA

 

Special coarse wood rasp texture ;-)

...Jim Thompson

 

Did you need any duct tape? ;-P

 

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

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

Thanks,
Rich

 

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

 

L-1011

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:...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.)