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Old 20th February 2015, 11:18 AM   #121
soekris is offline soekris  Denmark
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Just to close zero insertion or not:

There is a very good reason everybody is using zero insertion when upsampling.... A FIR filter is basically a large number of multiple add operation, and with each zero you can save a operation as zero multiplied by something is zero. So t.ex. upsampling from 44.1K to 352.8K is 1 input data and 7 zeroes inserted for each sample, if using something else than zero insertion you would need 8 times as many multiple add operation, cutting down on your filter length (number of taps)....
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Old 20th February 2015, 04:01 PM   #122
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Maybe this is an over simplification, but when people are reporting harshness with NOS filter it is during loud loud and intense passages. Couldn't this be due to the natural presentation of the music? When I am at a concert and music intensity increases so does distortion of instruments and stage gear, and sometimes it sounds very harsh. But that is the real tone of the music! I like NOS because it reveals tone signatures, good and bad.
To ask another way- do filters have a "soft-clipping" function?
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Old 20th February 2015, 04:50 PM   #123
TNT is offline TNT  Sweden
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In concert, close to the stage I think the ears can be distorted due to aboslute level. At playback, if the sound is hars at moderate levels its either the recording or the playback systen that is a fault. Ear distortion is not the reason in this case. Mic and recording equipment today has really low distorsion, even at very high sound pressur so on modern, well made recordings this "should" not be a problem. Remains the playback gear.

//
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Old 20th February 2015, 05:16 PM   #124
TNT is offline TNT  Sweden
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Input from latest discussions I made 2 versions of the MB2 filter. To be declared what within 4 hours.

I can say that the steepness is still there.

//
Attached Files
File Type: zip MB2a.skr.zip (5.6 KB, 42 views)
File Type: zip MB2b.skr.zip (5.5 KB, 48 views)
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Old 20th February 2015, 08:22 PM   #125
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Quote:
Originally Posted by lehmanhill View Post
I
From what John Swenson said about windowed sinc filters and interpolation, I wonder if this is possible in SoX? That said, he also implied that these things take a lot of space, so it may not be possible in the FPGA.

I will try to read deeper into the SoX documentation and try to understand.

Jac

sinc is a mathematically ideal lowpass filter with vertical cutoff and no ringing.

The equation is sinc = sin(pi * x)/(pi * x) which when plotted looks like:

Click the image to open in full size.

You should recognise the shape of the impulse from all the linear phase filters that have been posted to this thread.

While sinc is an ideal low pass filter, the ripples to each side continue to infinity. This is a problem when you have a limited number of poles/taps available. The DAM1021 can use 1016 taps/poles for 44.1 filters. If you simply truncate the ripples you get high levels of distortion.

This issue is addressed by applying a windowing function to the sinc filter.

Interpolation is a result of applying a low pass filter to the data.

There is a very good explanation of windowed-sinc here:
Strategy of the Windowed-Sinc
http://www.dspguide.com/CH16.PDF

All of this is basic DSP, so don't fall into the trap of thinking that SoX some magical piece of software simply because it has a celebrity endorsement.

cheers
Paul
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Last edited by spzzzzkt; 20th February 2015 at 08:40 PM.
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Old 20th February 2015, 08:38 PM   #126
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Quote:
Originally Posted by TNT View Post
In concert, close to the stage I think the ears can be distorted due to aboslute level. At playback, if the sound is hars at moderate levels its either the recording or the playback systen that is a fault. Ear distortion is not the reason in this case. Mic and recording equipment today has really low distorsion, even at very high sound pressur so on modern, well made recordings this "should" not be a problem. Remains the playback gear.

//
There was a fantastic free SACD produced by DPA Microphones around 2008 called "Miking a Grand Piano". It's intended to demonstrate different mic configurations, and has 8 or 9 tracks of the each performance captured with different setups. Because the recordings are intended to illustrate mic and array performance there is no additional effects or production applied. The music is not the most thrilling stuff you've ever listened to, but it is a very useful reference for judging system performance if you can track it down.

DAD - News Miking a Grand Piano - a Super Audio CD by DPA Microphones

I really need to find someone who can rip the SACD layer...
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Old 20th February 2015, 08:57 PM   #127
TNT is offline TNT  Sweden
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Interesting. I can not play SACD. My Philips SACD1000 broke which was a pity because it soundes really nice. So hopefully the DAM can do it. We need a solution to rip the SACD layer. Those Playstations are hard to get hold of I suppose.

Fortunantly there are really clean recordings, even on red book 44,1. I hope to be able to produce some own recordings this year using Acko's ESS based A/D board.

MB2b and DAM on battery is producing the cleanest I have heard the DAM yet. Time to reveal the filters..

//
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Old 20th February 2015, 09:05 PM   #128
TNT is offline TNT  Sweden
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I took the previosly posted MB2 filter and made the follwing modification to the text file. *No* change made in the generated coefficients!

(-- signature, samplerate, interpolationrate, type, numbercoefficients, multiplier)

MB2a: dam1021,44100,8,1,1016,7
MB2b: dam1021,44100,2,1,1016,1


MB2a: 7/8ths will create rounding error in estimating the levels of each sample but if there where clipping in the filter they should be gone. Almost full output level.

MB2b: Just 2x oversampling and no gian multiplication so no rounding errors. 6 dB down?

Thinking of a MB2c: 8x OS, mult=4. 6 dB down? Noise spreading and no rounding errors. I will post it.

//

Last edited by TNT; 20th February 2015 at 09:17 PM. Reason: 383->1016
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Old 20th February 2015, 09:16 PM   #129
TNT is offline TNT  Sweden
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MB2c: dam1021,44100,8,1,1016,4

Havent listen but will of cource.

//
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File Type: zip MB2c.skr.zip (5.5 KB, 35 views)
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Old 20th February 2015, 09:29 PM   #130
TNT is offline TNT  Sweden
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Dont forget to remove the RS232 cable after update - you do not want that computer ground in the DAM.

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