Rather than clogging up the main vendor thread with posts and discussion about alternative filters, it seems more useful to corral all the information into one spot.
My intention is to put together a collection of basic filters starting with:
I'll post up response curves measured directly from the filter parameters I post up, and ask anyone else contributing filters to do the same, to make comparisons more straight forward.
If anyone wants to contribute analog measurements of the filters they are welcome to do so.
cheers
Paul
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Recommended Filters as at 1 June 2015
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NewNOS
"Correct" NOS filter implementation for the DAM1021
http://www.diyaudio.com/forums/digi...filter-brewing-soekris-r2r-6.html#post4245752
EQHQ v1
Brick wall filter, allowing aliasing to 23.5kHz.
Based on the stock 44.1 filter, but heavily reworked based on recent forum filter research.
All other filters redesigned and updated.
http://www.diyaudio.com/forums/digi...ilter-brewing-soekris-r2r-23.html#post4342582
EQHQ_apo and _quasiapo
Minor variations of the EQHQ v1 which limits imaging to 22.05kHz and 22.5kHz respectively.
These are more strictly correct than the v1, and have a slightly smoother character.
http://www.diyaudio.com/forums/digi...ilter-brewing-soekris-r2r-24.html#post4343625
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Background Reading
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Test Tracks
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DPA Microphones - Miking A Grand Piano
Promotional CD illustrating techniques for miking a grand piano using their product range.
The was given away on request by DPA Microphones. This was released in 2007/8 and is long out of print.
Files are 44.1/16bit in .flac format and the zip archive is 270Mb.
As this is promotional material for DPA Microphones I believe there should be no issues sharing/spreading the word about DPA Microphones.
https://www.dropbox.com/s/223h1yuvlpx9s0u/DPA_MaGP_FLAC441.zip?dl=0
The SACD/CD contains 7 performances, with 8 different mic configurations.
1-8 Fallin' Leaves
9-16 Evening Song
17-24 Slowly Drifting
25-32 One for the New Ones
33-40 The Dat I Met Mr. Hayden
41-48 La Gazzellina
49-56 Minature XIV
The mic configurations are in the same order for each performance
1) 4041-SP, AB Stereo
2) 4006-TL, AB Stereo
3) 4052, In magnets on frame
4) 4011-TL, Bass/mid-treble positioned
5) 4021, ORTF Stereo
6) 4021, In magnets on frame
7) 4061, Hung from lid
8) 4061, In magnets on frame
The booklet that came with the disc can be download from the DPA site, but is mainly a discussion of miking techniques used.
http://www.dpamicrophones.com/en/Download/~/media/PDF/Download/grandpiano.pdf
My intention is to put together a collection of basic filters starting with:
- Linear-phase anti-aliasing
- Minimum-phase anti-aliasing
- Linear-phase soft roll-off
- Minimum-phase soft roll-off.
I'll post up response curves measured directly from the filter parameters I post up, and ask anyone else contributing filters to do the same, to make comparisons more straight forward.
If anyone wants to contribute analog measurements of the filters they are welcome to do so.
cheers
Paul
**********
Recommended Filters as at 1 June 2015
**********
NewNOS
"Correct" NOS filter implementation for the DAM1021
http://www.diyaudio.com/forums/digi...filter-brewing-soekris-r2r-6.html#post4245752
EQHQ v1
Brick wall filter, allowing aliasing to 23.5kHz.
Based on the stock 44.1 filter, but heavily reworked based on recent forum filter research.
All other filters redesigned and updated.
http://www.diyaudio.com/forums/digi...ilter-brewing-soekris-r2r-23.html#post4342582
EQHQ_apo and _quasiapo
Minor variations of the EQHQ v1 which limits imaging to 22.05kHz and 22.5kHz respectively.
These are more strictly correct than the v1, and have a slightly smoother character.
http://www.diyaudio.com/forums/digi...ilter-brewing-soekris-r2r-24.html#post4343625
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If people want to start then I now have the tools on our website:
http://www.soekris.dk/1021filt.txt -- ascii file with all filters
http://www.soekris.dk/1021filt.skr -- binary file for downloading onto a dam1021
http://www.soekris.dk/MKROM.EXE -- 32 bit dos utility to convert txt file to skr file, usage "mkrom 1021filt"
Please note that messing with IIR filters without knowing what you're doing can result in oscillations which will blow your speakers and/or ears.
The dam1021 FIR1 is operating at 352.8K/384K and each filter can have up to:
1016 tabs at 44.1K/48K input sample rate
508 tabs at 88.2K/96K input sample rate
252 tabs at 176.4K/192K input sample rate
124 tabs at 352.8K/384K input sample rate, but normally bypassed
FIR2 is operating at 2.822M/3.072M and can have up to 120 tabs, with input sample rates 352.8K/383K.
All upsampling is done by zero insertion, therefore gain need to be set to match oversampling rate.
There can be multiple of each filters in the 1021filt.txt filter file, but minimum one need to be there for each input sample rate. Currently just the first one for a given sample rate is used, in later firmware releases you will be able to choose between different filters.
Again, you need to know what you're doing if you want to do your own filters, it's not that simple and there aren't much error checking in the tools....
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Background Reading
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- Windowed-sinc filters (from The Scientist and Engineer's Guide to
Digital Signal Processing - Steven W. Smith, Ph.D.: http://www.dspguide.com/CH16.PDF - Anti-alias and anti-image filtering - Juilan Dunn: http://www.nanophon.com/audio/antialia.pdf
- Why do equalisers sound different? - Michael Gerzon: http://www.audiosignal.co.uk/Gerzon archive.html - download available in several formats.
- Ringing False: Digital Audio's Ubiquitous Filter - Keith Howard: Ringing False: Digital Audio's Ubiquitous Filter | Stereophile.com
- The Ayre MP Series (Digital filter white paper): https://www.ayre.com/pdf/Ayre_MP_White_Paper.pdf
- Theory of Upsampled Digital Audio - Doug Rife: http://www.mlssa.com/pdf/Upsampling-theory-rev-2.pdf
****************
Test Tracks
****************
DPA Microphones - Miking A Grand Piano
Promotional CD illustrating techniques for miking a grand piano using their product range.
The was given away on request by DPA Microphones. This was released in 2007/8 and is long out of print.
Files are 44.1/16bit in .flac format and the zip archive is 270Mb.
As this is promotional material for DPA Microphones I believe there should be no issues sharing/spreading the word about DPA Microphones.
https://www.dropbox.com/s/223h1yuvlpx9s0u/DPA_MaGP_FLAC441.zip?dl=0
The SACD/CD contains 7 performances, with 8 different mic configurations.
1-8 Fallin' Leaves
9-16 Evening Song
17-24 Slowly Drifting
25-32 One for the New Ones
33-40 The Dat I Met Mr. Hayden
41-48 La Gazzellina
49-56 Minature XIV
The mic configurations are in the same order for each performance
1) 4041-SP, AB Stereo
2) 4006-TL, AB Stereo
3) 4052, In magnets on frame
4) 4011-TL, Bass/mid-treble positioned
5) 4021, ORTF Stereo
6) 4021, In magnets on frame
7) 4061, Hung from lid
8) 4061, In magnets on frame
The booklet that came with the disc can be download from the DPA site, but is mainly a discussion of miking techniques used.
http://www.dpamicrophones.com/en/Download/~/media/PDF/Download/grandpiano.pdf
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