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Filter brewing for the Soekris R2R
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Old 11th March 2015, 10:43 AM   #351
zfe is offline zfe
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Quote:
Originally Posted by spzzzzkt View Post
This is my latest totalCRaP™ filter.

The key features are:
- 8x OS
- Linear Phase
- Steep roll-off and healthy amount of pre/post ringing.

So something to offend everyone - except perhaps TNT and zfe

The bonus feature here is:
- 3.5dB attenuation in FIR2 to provide headroom in the R2R. This will mainly benefit those not using the digital volume.

I've come across a post by Bruno Putzeys advising against use of NOS with the Hypex UcD modules as they have a 400kHz control loop, and the HF hash from NOS can interact leading to distortion in the amp. So NOS is off the menu for me as I was definitely hearing distortion even in the "sorted" NOS filters.

Please enjoy the sound of totalCRaP™...


Quote:
Originally Posted by soekris View Post
That depends.... Try expressing very small numbers in fixed point format, like some of the FIR coefficients....

But there are two things here:

1) The format that rePhase outputs, should be floating point with many digits as it don't know the actual hardware....

2) The format the actual hardware use, in case of the dam1021 it's 2.30 fixed point format for the FIR filters and 3.29 fixed point format for IIR filters. FPGA's are not good at floating point....

The mkrom utility read and process the input .txt parameter files as 64 bit floats, including the multiplier, then convert to the 2.30/3.29 fixed formats in the final step, which are pretty good, t.ex. the SigmaDSP chips use fixed 4.24 format for coefficients....

So any filter coefficients that for which coefficients x multiplier is smaller ~10^9 will be treated as zero by the DAM. There are a lot of such coefficients in your filter.

That does not mean that it is a bad filter, it is just equivalent to a shorter filter and the graphs of that will not exactly look as that what you get out of your design tools.

I have to admit I have not listend to it, as all my well known 16/44 material is in form of "silver disks" which I have not with me.
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Old 11th March 2015, 03:32 PM   #352
oneoclock is offline oneoclock  Europe
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What type are the totalCRaP™ F2 filters?
And 48, 88,96, etc?

Last edited by oneoclock; 11th March 2015 at 03:39 PM.
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Old 11th March 2015, 06:13 PM   #353
zfe is offline zfe
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Originally Posted by zfe View Post
... smaller ~10^9 ...
That should have been 10^{-9} of cause.
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Old 11th March 2015, 07:22 PM   #354
nusa is offline nusa  Italy
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Quote:
Originally Posted by spzzzzkt View Post
This is my latest totalCRaP™ filter.


Please enjoy the sound of totalCRaP™...
OK, I gave it a try. Well thanks, but this one is really not for me... After some songs I had to go back to the NOS one.
With your CRaP, I had to lower the volume a lot (but from what you wrote I understood that it should have been the exact opposite)
And, female voices are really forward, contrary to the NOS filter.
But please, keep up with the good work!!

For info the DAM is connected to a Mark Levinson not a hypex and no cans here.
Ciao
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Old 11th March 2015, 08:03 PM   #355
spzzzzkt is offline spzzzzkt  Australia
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Quote:
Originally Posted by oneoclock View Post
What type are the totalCRaP™ F2 filters?
And 48, 88,96, etc?
44.1 and 48khz.
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Old 11th March 2015, 08:46 PM   #356
spzzzzkt is offline spzzzzkt  Australia
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Quote:
Originally Posted by nusa View Post
OK, I gave it a try. Well thanks, but this one is really not for me... After some songs I had to go back to the NOS one.
With your CRaP, I had to lower the volume a lot (but from what you wrote I understood that it should have been the exact opposite)
And, female voices are really forward, contrary to the NOS filter.
But please, keep up with the good work!!

For info the DAM is connected to a Mark Levinson not a hypex and no cans here.
Ciao
The "correct" NOS is rolled off in the HF.

The two images attached are of the NOS filter co-efficents applied to gaussian white noise file. Because the white noise has a flat spectrum this allows you to determine the response of the filter. Treat -40dB as 0dB. The NoS filter is -1dB at 14kHz, and -3dB at 20kHz. As Eldam and others pointed out the totalDAC uses a FIR filter to correct for this roll-off so isn't a 100% pure NOS DAC.

In contrast the first totalCRaP filter is pretty well flat out to 19kHz, so will have more HF energy above 12-13kHz. So it's not really forward, just not rolled off.

The 3.5dB headroom will potentially reduce harshness with near full-scale signals if you are using an OS filter, and fixed 0dB output.
Attached Images
File Type: png NOS_1s.png (91.2 KB, 359 views)
File Type: png NOS_1s_zoom.png (102.6 KB, 350 views)
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Old 11th March 2015, 08:54 PM   #357
spzzzzkt is offline spzzzzkt  Australia
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Quote:
Originally Posted by spzzzzkt View Post
44.1 and 48khz.
Sorry misread the question. These two are done with Octave's FIR1 function.

FIR2 is default but with multiplier reduced from x8 to x6.8333 to give 3.5dB "headroom" for the R2R ladder.
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Old 11th March 2015, 08:59 PM   #358
nusa is offline nusa  Italy
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Quote:
Originally Posted by spzzzzkt View Post

In contrast the first totalCRaP filter is pretty well flat out to 19kHz, so will have more HF energy above 12-13kHz. So it's not really forward, just not rolled off.

The 3.5dB headroom will potentially reduce harshness with near full-scale signals if you are using an OS filter, and fixed 0dB output.
Well, now that you are explaining it this way, perhaps I'm realizing that I've done a fundamental mistake. Indeed I also process the musical message through DIRAC. Therefore if I listen to a new filter that alter the response in the various frequencies, I should also consider redoing all measurements... The fact that I use Dirac is maybe the reason why my listening experience Is completely different then the general opinion here.... Fascinating...

Last edited by nusa; 11th March 2015 at 09:05 PM.
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Old 11th March 2015, 09:38 PM   #359
Mark Verhoeven is offline Mark Verhoeven  Netherlands
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Quote:
Originally Posted by nusa View Post
Well, now that you are explaining it this way, perhaps I'm realizing that I've done a fundamental mistake. Indeed I also process the musical message through DIRAC. Therefore if I listen to a new filter that alter the response in the various frequencies, I should also consider redoing all measurements... The fact that I use Dirac is maybe the reason why my listening experience Is completely different then the general opinion here.... Fascinating...
The differences in sound between 2 filters should be the same with or without Dirac. Why don't you bypass the Dirac processing and compare the sound of both filters again?
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Old 11th March 2015, 09:44 PM   #360
nusa is offline nusa  Italy
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Quote:
Originally Posted by Mark Verhoeven View Post
The differences in sound between 2 filters should be the same with or without Dirac. Why don't you bypass the Dirac processing and compare the sound of both filters again?
Indeed I should, the weekend is not so far away... And BTW, I will soon have a Tortuga passive preamplifier. It will be interesting to see how much the digital volume Is compromising the sound quality.
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