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Old 16th February 2015, 06:11 PM   #61
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Yes, the hardware filters probably remove the nasty artifact that get out of in minimum phase filter processing.
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Old 16th February 2015, 06:13 PM   #62
TNT is offline TNT  Sweden
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I dont think it is a phase caracteristcs issue. Rather simply how steep the filters are.

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Old 16th February 2015, 06:42 PM   #63
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Great thread. Just startet "reading" up on the subject

Good information in the first post and more information here
Filters and You: FIR Filters - Tuts+ Music & Audio Tutorial

BTW: Is "rephase" THE tool to use?

Can I use for instance audacity to see the impulse result from "rephase" simulation?

For the record..
Totally newbie in this.. But hopefully a quick learner..

Last edited by bambadoo; 16th February 2015 at 06:47 PM.
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Old 16th February 2015, 06:46 PM   #64
Eldam is offline Eldam  France
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Just here on DIYA, Abraxilo on him DIYAUDIO blog published a simple filter for NOS 16/41 material with smd components, but don't remember if it's after a buffer or at the output of a multibitdac passive i/v of a TDA1387 !
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Old 16th February 2015, 07:45 PM   #65
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Quote:
Originally Posted by bambadoo View Post
Great thread. Just startet "reading" up on the subject

Good information in the first post and more information here
Filters and You: FIR Filters - Tuts+ Music & Audio Tutorial

BTW: Is "rephase" THE tool to use?

Can I use for instance audacity to see the impulse result from "rephase" simulation?

For the record..
Totally newbie in this.. But hopefully a quick learner..
You need something that will output filter coefficients in .txt format. rePhase is probably the easiest most accessible tool that does that.

TNT's friend looks to be using something like MATLAB or Octave. MATLAB has a filter design plugin which unfortunately hasn't been ported to Octave, but Octave can be used if you know the parameters required.
http://vdl2-ase.wikispaces.com/HowTo...+in+GNU+Octave

There are commercial tools like ScopeFIR if you want to outlay a couple of hundred $US:
ScopeFIR: FIR Filter Design Software for Windows | Iowegian International

cheers
Paul
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Old 16th February 2015, 09:42 PM   #66
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Quote:
Originally Posted by Algar_emi View Post
Yes, the hardware filters probably remove the nasty artifact that get out of in minimum phase filter processing.
"Nasty" is such an emotive term.

It's worth having a read of Doug Rife's paper on Oversampling Theory (link in the first post). There is an interesting section "Upsampling ameriolates differential non-linearity".

Quote:
Upsampling provides another method for averaging away differential non-linearity but without requiring multiple DACs. The ultrasonic image energy that a slow roll-off anti-imaging filter presents to the DAC can be thought of as a form of dither. As mentioned above, the image spectrum is folded which has the effect of de-correlating it from the baseband audio signal thus making it random for all practical purposes.
Quote:
Eventually, the ultrasonic energy is filtered out, first by a low-order analog filter, then the power amplifier, the loudspeakers, the air in the room and finally by the ear. This post- DAC low pass filtering can be thought of as an averaging operation.
Rife concludes:
Quote:
The sound quality of 44.1 kHz digital audio data can be dramatically improved by employing a “poor” oversampling digital anti-imaging filter having a slow roll-off in place of a “good” digital filter having a fast roll-off and a high stop band attenuation. It was shown that the ultrasonic images output by this “poor” filter is responsible for the improved sound quality, reducing certain forms of non-linear distortion such as that due to the differential non-linearity found in all DACs. There may very well be other, subtler, forms of non-linear distortion in DACs, which may also be reduced by signal-dependent ultrasonic dither.
For context, in the preceding section Rife notes that
Quote:
... distortion due to differential non-linearity in multibit DACs tends to increase during loud musical passages, which can obscure low-level detail and result in a subjectively grainy, harsh and sterile sound.
So it could well be that the predilection for sharp roll-off filters contributes in part to the harshness that some have reported. It would be interesting to explore Rife's theory and see how it can be applied in practice.

His observations about the filtering effect of air is worth taking into account, as there will be differences between headphones, close monitoring, and sitting 3 metres from the speakers. It's worthwhile having a play with the calculator at http://www.sengpielaudio.com/calculator-air.htm

At 25C and 50% humidity, the attenuation per metre is:

10kHz : 0.147dB/m
15kHz : 0.306dB/m
20kHz : 0.502dB/m
25kHz : 0.717dB/m
30kHz : 0.937dB/m

With headphones the attenuation will essentially be 0dB across the spectrum, near-field monitoring (say 1 metre) a slight roll off, but by 3 metres the effect becomes far more significant with a -2.8dB roll-off at 30kHz.

cheers
Paul

Last edited by spzzzzkt; 16th February 2015 at 10:07 PM.
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Old 16th February 2015, 09:58 PM   #67
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Dear Paul, thanks for your work in this thread and the filters. One note, the link for "Sampling, Oversampling, Imaging and Aliasing" seems broken.
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Old 16th February 2015, 10:18 PM   #68
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Quote:
Originally Posted by PanagiotisPapadakos View Post
Dear Paul, thanks for your work in this thread and the filters. One note, the link for "Sampling, Oversampling, Imaging and Aliasing" seems broken.
Thanks, fixed.
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Old 16th February 2015, 11:14 PM   #69
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Originally Posted by TNT View Post
spzzzzkt is right on the money.

I still feel that the D/A is not as clean in the upper regions as I would have wished - at times it has a little grey hash. See if the unbuffered output provides a solution. Also for these filters I need to hear them over loudspeakers - hopefully this week.
//
TNT, what is your power supply?
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Old 16th February 2015, 11:17 PM   #70
TNT is offline TNT  Sweden
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SMPS. Meanwell. I also have batteries. Will try these again. Good that you reminded me. Listening this evening I wasn't to thrilled.

//
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