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PostPosted: Thu Aug 28, 2014 8:28 pm 
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Dog
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ball3901 wrote:
AHA!!!

I am glad I found this 'diagram' As one of those left-handed, right brained people, I am excessively visual, and this was most helpful.

http://www.accuphase.com/cat/dp-700_e.pdf


Wait a minute... how is that "digital volume processing" done?
This doesn't smell right.
Alas, it smells like PCM.

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PostPosted: Thu Aug 28, 2014 10:07 pm 
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carlosfm wrote:
ball3901 wrote:
AHA!!!

I am glad I found this 'diagram' As one of those left-handed, right brained people, I am excessively visual, and this was most helpful.

http://www.accuphase.com/cat/dp-700_e.pdf


Wait a minute... how is that "digital volume processing" done?
This doesn't smell right.
Alas, it smells like PCM.



Yup. I wasn't interested in 'that' part... :) Accuphase is pulling one over on us.... hehe

It is the visual of the 'moving average' filter that was the 'aha' moment.


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PostPosted: Fri Aug 29, 2014 12:50 am 
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Benjamin
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Quote:
Ultra Jitter-Free Plus PLL circuit
:rolleyes:


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PostPosted: Fri Aug 29, 2014 10:45 am 
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Muriel
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Hi,

ball3901 wrote:
BB FIR filter for DSD. In order for the filter to work, 1-bit DSD has to be "transformed" into 8 bit/9level thermometer coding. Dynamic Element Matching is performed at the same time...

Or, like with the Signalyst DAC, 32bit/33 level thermometer coding, DEM, etc. etc. etc.


I would not call the result of this filter Multi-Level coding.

The respective coefficients for the BB FIR Filter are not thermometer code. THey have non equal resistors at all 8 stages. This way they keep the compromise between impulse response distortion and filtering on the good side.

The "impulse distortion" is confined to 8BCK periods, even at single rate DSD, that is under 3uS (equivalent to 160K sine wave). With an actual relatively steep analogue filter at around 80KHz added this analogue filter dominates the impulse response (as can be seen on the 'scope) and thus the results appears at the output as that of fundamentally a pure analogue filter, but with greater suppression of out of band noise than would be possible with only the analogue filter.

A bit of very clever engineering by BB.

Now, if we make the window of the filter longer (16, or even 32 BCK periods) the effective filter corner of the FIR filter (and thus it's impact on the impulse response) moves down in the frequency domain and to a longer time of impulse distortion in the time domain to a point where the FIR filter Impulse response (with it's symmetrical pre- and post-ringing) dominates over any analogue filter, at least for single speed DSD.

It is all a tradeoff and in my view BB made the correct call back then. In principle they could have created a 64BCK delay chain with unitary weighting for each elemnt (that is double of what the Signalyst DAC does), but they felt that so much impulse distortion was undesirable.

Ciao T

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PostPosted: Fri Aug 29, 2014 3:37 pm 
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Cow

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Kuei Yang Wang wrote:
Hi,

ball3901 wrote:
BB FIR filter for DSD. In order for the filter to work, 1-bit DSD has to be "transformed" into 8 bit/9level thermometer coding. Dynamic Element Matching is performed at the same time...

Or, like with the Signalyst DAC, 32bit/33 level thermometer coding, DEM, etc. etc. etc.


I would not call the result of this filter Multi-Level coding.

The respective coefficients for the BB FIR Filter are not thermometer code. THey have non equal resistors at all 8 stages. This way they keep the compromise between impulse response distortion and filtering on the good side.

The "impulse distortion" is confined to 8BCK periods, even at single rate DSD, that is under 3uS (equivalent to 160K sine wave). With an actual relatively steep analogue filter at around 80KHz added this analogue filter dominates the impulse response (as can be seen on the 'scope) and thus the results appears at the output as that of fundamentally a pure analogue filter, but with greater suppression of out of band noise than would be possible with only the analogue filter.

A bit of very clever engineering by BB.

Now, if we make the window of the filter longer (16, or even 32 BCK periods) the effective filter corner of the FIR filter (and thus it's impact on the impulse response) moves down in the frequency domain and to a longer time of impulse distortion in the time domain to a point where the FIR filter Impulse response (with it's symmetrical pre- and post-ringing) dominates over any analogue filter, at least for single speed DSD.

It is all a tradeoff and in my view BB made the correct call back then. In principle they could have created a 64BCK delay chain with unitary weighting for each elemnt (that is double of what the Signalyst DAC does), but they felt that so much impulse distortion was undesirable.

Ciao T



Indeed. But, some people as has been mentioned more times than I can remember, do see it as multi level code, especially if the elements are equally weighted 'thermometer' code. And whether the elements are equal or not, you could send a multi-bit delta sigma code into the filter just as well, or so I think anyway. You could moving average 'shift' multi-bit delta sigma with different delays.


It really does seem like semantics, though. It is a method for filtering a one bit signal. Or multi-bit. In the end, it is just a filter.


I think I once saw John Swenson call this kind of filter a hybrid. I think that makes sense. The delay chain is digital. The application of the coefficients is digital to analog conversion. The output is a filtered analog summation of the 8 elements.


I will say this, though. I am now starting to see how the Lampizator type of DSD conversion is so very very simple!! Yes, I DO think I could build a DSD DAC. Asynch USB receiver, some kind of reclocking, and construct a simple analog filter and gain stage.

I get it now...


Andrew


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PostPosted: Fri Aug 29, 2014 5:19 pm 
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Muriel
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Hi,

ball3901 wrote:
It really does seem like semantics, though. It is a method for filtering a one bit signal. Or multi-bit. In the end, it is just a filter.

I think I once saw John Swenson call this kind of filter a hybrid.


I'd call it "digilogue". The kind of delay based lowpass filter exists in the purely analogue world. Certain types of Colour TV decoders (that was in the days when TV and Movies were analogue of course) contained a surface wave acoustics device (SAW-Devince - called a delay line) which formed a mechanical delay line for the analogue TV signals and multiple taps were used to create similar style delay line filters, there IIRC to separate the colours (so bandpass).

As the delay is in the digital domain (as our signal is conveniently digital), it is digital delay but as the filtering is strictly analogue and in the Analogue Domain - digilogue.

ball3901 wrote:
I will say this, though. I am now starting to see how the Lampizator type of DSD conversion is so very very simple!! Yes, I DO think I could build a DSD DAC. Asynch USB receiver, some kind of reclocking, and construct a simple analog filter and gain stage.


Toldcha. It is so easy even bankers with no formal training in electronics can do it...

Ciao T

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