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Old 30th June 2004, 01:04 AM   #21
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Default Re: Re: Re: The little glue loggic is a problem for Jitter, ..

Quote:
Originally posted by jbokelman
rfbrw, a serial adder wont work for digital audio. With 16-bit samples, the largest negative value is 32768. The twos-complement, +32768, cannot be represented in 16 bits. In fact, the twos-complement of 32768, as represented in 16 bits, is 32768. To correct this anomaly, every sample that equals 32768 after the addition must be changed to +32767.
I am aware of the imbalance between the number of negative and positive values and that can be addressed in the serial domain.
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Old 30th June 2004, 01:23 AM   #22
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Quote:
Originally posted by Bricolo
jbokelman, add a DC offset to an AC signal

then, measure the distortion of this signal, after a (perfect) coupling cap
the distortion is zero

that's the same here

your math is wrong, you are reasoning in a/b instead of a-b
You need to study your number formats in order to appreciate what's going on here. Two's comp inversion requires the addition of the value one. Its fundamental to the working of this number format. If you do not add the one, you are one bit off compared to the original.
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Old 30th June 2004, 01:35 AM   #23
Bricolo is offline Bricolo  France
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of course you're one bit off

but as guido said, it's just an offset
this ain't distortion!
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Old 30th June 2004, 02:14 AM   #24
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Quote:
Originally posted by Bricolo
of course you're one bit off

but as guido said, it's just an offset
this ain't distortion!
If a value isn't what it is supposed to be, then it is distorted.
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Old 30th June 2004, 06:35 AM   #25
Werner is offline Werner  Europe
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Quote:
Originally posted by rfbrw


If a value isn't what it is supposed to be, then it is distorted.
AFAIK, that is untrue.


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Old 30th June 2004, 01:28 PM   #26
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Maybe this is the soloution:

1.) one DAC with normal data
2.) 2nd DAC with inverted data-signal in I2S
3.) a Resistor that adds (nearly) the Current of 1 LSB to the output of the 2nd DAC ...
3b.) Instead of the Resistor you could add a 3rd DAC that outputs permanently +1LSB :-)

Or:
You are building caps in the signalpath ...
(The 1LSB is DC ...)


CYa

Jobstens
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Old 30th June 2004, 03:07 PM   #27
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Default CLARIFICATION

Going back to the 4-bit DAC example: With the sample sequence 2, 4, the output of the DAC will double from one sample to the next. The amount of change for that sample period is 6dB. The inverted samples are -3, -5. The output of the inverted DAC, for the same sample period, will change in the proportion 3:5 or 4.4dB. A signal that changes 4.4dB between two specific points in time is not the same shape as a signal that changes 6dB between the same two points. That difference is distortion.

You can figure out what happens with the sample sequence -2, -4.

Adding a bit to each sample in the digital domain results in distortion and I dont think that distortion can be removed by adding a DC offset in the analog domain. Note: I make a distinction between adding a DC offset, after the fact, that is, after I/V conversion, verses biasing the DAC, which in effect, adds a 1-bit offset at the point of conversion, which is, arguably, still in the digital domain.

The point is, DAC designers, who simply invert the data stream to get an inverted output, rarely, if ever, bias the DAC so that a -1 digital input results in 0 analog output. As a consequence, their DACs have 6dB of additional distortion. Either they dont know about it and dont hear it or they know about it and dont care.
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Old 30th June 2004, 04:51 PM   #28
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Quote:
Originally posted by Calimero
So what will result in more distortion the glue-logic or the inversion?
Inversion. The logic that performs the twos-complement works on all 16 data bits in parallel and has no influence on the clocks that control the DAC.

Quote:
Originally posted by rfbrw I am aware of the imbalance between the number of negative and positive values and that can be addressed in the serial domain.
How does the serial inverter/adder know, at the moment it sees the LSB, what the following bits will be so, if necessary, the invert/adder can replace the maximum negative integer with the maximum positive integer?
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Old 30th June 2004, 07:34 PM   #29
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this is done by DENON DAP-5500. They know what they do ...

Regards

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Old 30th June 2004, 08:16 PM   #30
Bricolo is offline Bricolo  France
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Quote:
Originally posted by Werner


AFAIK, that is untrue.


you smartass!


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