DSP Xover project (part 2)
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chaparK
diyAudio Member

Join Date: Apr 2010
Location: Luxembourg
Quote:
 Originally Posted by paalj That was an interresting lesson. Even if most of it went over my head, I think I got the basic picture.
Yes these are great DSP classes!! The professor talking there is Oppenheim himself. He co-authored with Schafer what became the Number 1 textbook on digital signal processing during many years. It's dating a bit now, but it's still absolutely relevant. There are other videos that I recommend watching if you're interested in DSP.

Coming back to your question, let's take a simple example of an analogue low-pass LR4 cutting at 10 kHz.
At 10 kHz, the filter is attenuating the input signal by 6 dB. You're OK with this, right?

Let's agree that the slope of the filter is 24 dB/oct straight after the corner frequency (it's not exactly the case, but it doesn't matter here).
This would mean that at 20 kHz, your analogue filter is attenuating the signal by 6+24 = 30 dB.
At 40 kHz, attenuation equals 6+24+24 = 54 dB.
At 80 kHz, attenuation equals 6+24+24+24 = 78 dB.
Etc.

You notice that the theoretical analogue model is not limited in frequency.

When you translate an analogue filter for the digital domain, sampling comes in with the problem that the system is limited in frequency. If you sample say at 48 kHz, then any frequency above Nyquist = 48 kHz/2 has no meaning.
With a system sampling at 48 kHz, we can't specify an attenuation by 54 dB at 40 kHz - it's just impossible.

This gives you an intuitive hint that digital realization of analogue filters are only approximations of the theoretical analogue model.
__________________
Najda DSP

 29th March 2013, 02:52 PM #752 chaparK   diyAudio Member   Join Date: Apr 2010 Location: Luxembourg The new release is available for download at the usual place. It includes a FW update as well, so this will reset your board to the factory settings. Make sure not to pull off the USB cable or the power chord while the new FW is being transferred __________________ Najda DSP
paalj
diyAudio Member

Join Date: Nov 2005
Location: Norway
Quote:
 Originally Posted by chaparK Yes these are great DSP classes!! The professor talking there is Oppenheim himself. He co-authored with Schafer what became the Number 1 textbook on digital signal processing during many years. It's dating a bit now, but it's still absolutely relevant. There are other videos that I recommend watching if you're interested in DSP. Coming back to your question, let's take a simple example of an analogue low-pass LR4 cutting at 10 kHz. At 10 kHz, the filter is attenuating the input signal by 6 dB. You're OK with this, right? Let's agree that the slope of the filter is 24 dB/oct straight after the corner frequency (it's not exactly the case, but it doesn't matter here). This would mean that at 20 kHz, your analogue filter is attenuating the signal by 6+24 = 30 dB. At 40 kHz, attenuation equals 6+24+24 = 54 dB. At 80 kHz, attenuation equals 6+24+24+24 = 78 dB. Etc. You notice that the theoretical analogue model is not limited in frequency. When you translate an analogue filter for the digital domain, sampling comes in with the problem that the system is limited in frequency. If you sample say at 48 kHz, then any frequency above Nyquist = 48 kHz/2 has no meaning. With a system sampling at 48 kHz, we can't specify an attenuation by 54 dB at 40 kHz - it's just impossible. This gives you an intuitive hint that digital realization of analogue filters are only approximations of the theoretical analogue model.
Hi Nick,
Thanks,
So basically changing my samplerate to 96kHz solved my problems

Quote:
 Originally Posted by chaparK The new release is available for download at the usual place. It includes a FW update as well, so this will reset your board to the factory settings. Make sure not to pull off the USB cable or the power chord while the new FW is being transferred
Great!
The update went well. Can you tell a bit about the flexibility of the FIR taps?

best,
Paal

 29th March 2013, 05:28 PM #754 Speedysteve7   diyAudio Member     Join Date: Dec 2009 Location: Hants/Berkshire/Surrey Yep - Update went like clockwork. Problem of no sound on about half of Setup swaps and connects / disconnects fixed. Now I can evaluate different setups much more easily. I'd better get another LED. Nice one Last edited by Speedysteve7; 29th March 2013 at 05:35 PM.
JLOP
diyAudio Member

Join Date: Sep 2011
Location: Luxembourg
Sample rate

Quote:
 Originally Posted by paalj So basically changing my samplerate to 96kHz solved my problems
It's getting more and more appealing

Just for my understanding, doesnt the max samplerate 192kHz give the best sound quality ? Is there a reason to stay on 96 kHz (save processor resources or whatsoever)?

BR
Jean-Louis

paalj
diyAudio Member

Join Date: Nov 2005
Location: Norway
Quote:
 Originally Posted by JLOP It's getting more and more appealing Just for my understanding, doesnt the max samplerate 192kHz give the best sound quality ? Is there a reason to stay on 96 kHz (save processor resources or whatsoever)? BR Jean-Louis
Hi Jean-Louis,
My processor load is 49 and 52% so I guess it will be overload?
I will try later

best,
Paal

 29th March 2013, 07:09 PM #757 RickDangerous   diyAudio Member   Join Date: Mar 2013 Location: Guanajuato, Mexico Anyone here who has the Najda care to review it on the following thread, please ? WAF Audio Najda reviews Thanks a lot
Speedysteve7
diyAudio Member

Join Date: Dec 2009
Location: Hants/Berkshire/Surrey
Quote:
 Originally Posted by JLOP It's getting more and more appealing Just for my understanding, doesnt the max samplerate 192kHz give the best sound quality ? Is there a reason to stay on 96 kHz (save processor resources or whatsoever)? BR Jean-Louis
I preferred the sound / presentation of 96KHz. I did those tests before I applied my crossovers and some correction.
192 sounded glassy and artificial. 48 sounded rather lowfi. 96 was sweet and pretty much transparent comparing A/B to my passives.
Slightly different presentation but pleasing.

I am at 52% and 47% load currently.

Last edited by Speedysteve7; 29th March 2013 at 07:41 PM.

 29th March 2013, 07:47 PM #759 RickDangerous   diyAudio Member   Join Date: Mar 2013 Location: Guanajuato, Mexico What filters are available on the Najda ? I can't find a manual anywhere and the site has virtually no information whatsoever. Thx
Shaun
diyAudio Member

Join Date: Aug 2001
Location: Cape Town, South Africa
Quote:
 Originally Posted by RickDangerous What filters are available on the Najda ? I can't find a manual anywhere and the site has virtually no information whatsoever.
Virtually any filter. You can find some info here WAF - Wroclaw Audio Force and in the rest of this thread.
__________________
Shaun Onverwacht
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