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Old 6th April 2013, 05:35 PM   #831
Shaun is offline Shaun  South Africa
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Quote:
Originally Posted by rubofdagreen View Post
As far as sampling rate goes I know less than nothing about FIR filters go.
When generating the coefficients you must specify the same sampling rate that you selected for Najda (48kHz/96kHz/192kHz), or the coefficients will not map to the correct frequencies when imported into Najda.
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Old 6th April 2013, 06:25 PM   #832
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Quote:
Originally Posted by Shaun View Post
When generating the coefficients you must specify the same sampling rate that you selected for Najda (48kHz/96kHz/192kHz), or the coefficients will not map to the correct frequencies when imported into Najda.
So the Najda does not accept 44.1 Khz natively. It does, however, convert the 44.1 into 48 Khz, correct ?
Is that a good idea ? I mean, THE audio source is the CD @ 44.1 Khz, or files ripped from CD and still usually at 44.1 Khz.
48 Khz is a professional sampling rate in...video, not home audio nor pro audio.
Wouldn't the signal be better untouched and left at 44.1 Khz ?
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Old 6th April 2013, 06:29 PM   #833
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Originally Posted by RickDangerous View Post
So the Najda does not accept 44.1 Khz natively. It does, however, convert the 44.1 into 48 Khz, correct ?
Is that a good idea ? I mean, THE audio source is the CD @ 44.1 Khz, or files ripped from CD and still usually at 44.1 Khz.
48 Khz is a professional sampling rate in...video, not home audio nor pro audio.
Wouldn't the signal be better untouched and left at 44.1 Khz ?
(Personally i am planning to enter the Najda digitally, since my source is most likely to be digital, i don't use cassettes or tape, and although i have hundreds of vinyls and a decent turntable i don't use them. My digital source will be the PC or my 24 track recorder, both of which will be running most of the time at 44.1).
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Old 6th April 2013, 11:09 PM   #834
chaparK is offline chaparK  Luxembourg
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Quote:
Originally Posted by RickDangerous View Post
(Personally i am planning to enter the Najda digitally, since my source is most likely to be digital, i don't use cassettes or tape, and although i have hundreds of vinyls and a decent turntable i don't use them. My digital source will be the PC or my 24 track recorder, both of which will be running most of the time at 44.1).
I wouldn't worry too much about sample rate conversion.

Quote:
Originally Posted by rubofdagreen View Post
MrDangerous plan on 100 plus the power supply and the case. That way you won't be cussing me. As far as sampling rate goes I know less than nothing about FIR filters go.
I had a look a the application you have used so far, and suggest you just try rePhase (as recommended by a few forum members):

rePhase | Free Audio & Video software downloads at SourceForge.net

Not sure whether you need this, but here's a simple example: I want to design a 3-way FIR crossover that mimics LR 48 dB/oct. (it's just a simple example in order to illustrate, don't ask me why LR 48 dB/oct ). I want one crossover at 400 Hz and another at 4 kHz.

So let's open rePhase and build this crossover together.

rehase1.png

I've circled the important fields.
On the right, from top to bottom:
- The number of taps. More taps will allow you achieving a better approximation, at the expense of increased DSP load.
- The rate: select here 48 kHz (select the same in Najda).
- Format: 32-bit float txt. With this option selected, generated files are compatible with Najda.
- Filename: make sure to save your file under a proper name

On the left, select the 'Linear Filters' tab.
We generate first the low-pass coefficients. I've selected here 511 coefs, and rePhase signals a max deviation of about 2dB with regard to the LR model. Yeah why not. Let's keep it.

Now we generate the bandpass:
rehase2.png
I've tried another number of taps (911). This time max deviation is only 0.22 dB. Fair enough.

Finally we generate the high-pass:
rehase3.png
In the high frequencies, I know I need less taps. I've tried 121 and it seems fine, with a max deviation of 0.00...

Now I can load the files in Najda Under Control:

rephase4.png

I can check the plots in Najda:

rephase5.png

Well it's crossing at 400 Hz and at 4 kHz, so we're happy aren't we?

What would be the sum?

rephase6.png

Oh no! what is that???

Alright, that's a time-alignment issue because filters have different lengths (= different numbers of taps).

Looking again at the 3 rePhase screenshots, we can see that:
- The low-pass has an offset of 256 samples
- The band-pass has an offset of 456 samples
- The high-pass has an offset of 61 samples.
We need to compensate for that.

The band-pass has the largest offset = largest delay. We leave it as is.
Then the low-pass requires a delay of 456-256 = 200 samples.
And the high-pass requires a delay of 456-61 = 395 samples.

rephase7.png

Now we can check the sum again. Make sure to check "Include Delay in Phase".

rephase8.png

So it's not perfectly flat because we didn't have perfect LR filters at the start.
Anyway, looking at the scale, the residual dip is quite small.

(Note:
In Najda's graph view:
- Click and drag to move the 0dB line up and down.
- Click+mouse wheel to zoom in/out
- Double click to reset the graph to original view)

Alright, we've here approximated a LR network. We could actually approximate anything (anything reasonable). You could load in rePhase your measurements, build a crossover and add EQing...

Hope this helps.

Nick
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Old 7th April 2013, 05:02 AM   #835
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If you use the digital outputs and an external DAC, would it be possible to send that analogue signal back to Najda-board (via the OP sockets I presume) and then use that for volume control?

br
Rickard
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Old 7th April 2013, 05:48 AM   #836
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Thanks Najda. When i am in Europe (August) i will order the board etc. I will be making speakers hopefully. And if it gets commercial i will be in touch with you!
Great board, well done.
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Old 7th April 2013, 09:29 AM   #837
chaparK is offline chaparK  Luxembourg
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Quote:
Originally Posted by rikkitikkitavi View Post
If you use the digital outputs and an external DAC, would it be possible to send that analogue signal back to Najda-board (via the OP sockets I presume) and then use that for volume control?

br
Rickard
Hi Rickard,

Actually yes, you could do that. CS3318 is flexible enough with signal swing on its input.

To route your DACs' outs to Najda, you could use either the amps sockets as you said - or just remove the decoupling capacitor that follows each output stage and inject your signal here.

Best,

Nick
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Old 7th April 2013, 09:52 AM   #838
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Quote:
Originally Posted by RickDangerous View Post
Thanks Najda. When i am in Europe (August) i will order the board etc. I will be making speakers hopefully. And if it gets commercial i will be in touch with you!
Great board, well done.
I meant Nick, not Najda, sorry!
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Old 7th April 2013, 09:59 AM   #839
ChrisPa is offline ChrisPa  United Kingdom
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Quote:
Originally Posted by rikkitikkitavi View Post
If you use the digital outputs and an external DAC, would it be possible to send that analogue signal back to Najda-board (via the OP sockets I presume) and then use that for volume control?

br
Rickard
Sorry for being dumb, but what do you propose will control the volume?
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Old 7th April 2013, 10:45 AM   #840
Ryssen is offline Ryssen  Sweden
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Quote:
To route your DACs' outs to Najda, you could use either the amps sockets as you said - or just remove the decoupling capacitor that follows each output stage and inject your signal here.
Do you have a schema of it,it would be easier to see.
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