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jiiteepee
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Joined: Mar 21 2007 - 6:14am
Phono RIAA EQ filter (evaluation version available)

Hello!

I hope this is the right sub-forum to place this thread into (as this is related to PC audio as well).

Maybe you're familiar already w/ the "new method" described @ EnhancedAudio.com pages.

Well, after many tries w/ not so good results in using various EQ plugins and standalone EQ software for RIAA compensation, I have now started implementing a solution of my own (similiar w/ the enhancedaudio's) ... a RIAA reproduction filter to be used when turntable is connected into soundcard without hardware RIAA stage in signal path .. but just through a flat pre-amp. I've seen there some commercial solutions available and one 'open source' solution for Soundblaster/kX users (link given below).

All I can say so far, is that the results I get here are really qood (especially w/ 88.2kHz and 96kHz filters) but, since I have only one set of hardware to evaluate this software, I would like you to evaluate this too. This version of filter,

( .. Sorry 'bout the visual outlook but ... don't laugh, it should work well)

which I have linked below, is prepared only for this evaluation purpose. It's optimized for 44.1 kHz audio (any bit depth can be used), it's for output only and it can be used through Cycling74 Max/MSP runtime enviroment only. ASIO, MME, DS, etc. are supported as well as Windows XP and MAC OS/X 10.3.9-> (there is a runtime for both systems available). For this "evaluation" version, I have included a rumble filter (Subsonic) w/ ability to set the cutoff frequency (5-30Hz) and Q (0.1-1.41). It's allways switched "ON" and not very well implemented (see below).

Here are listed the needed software:
RIAA Filter (for 44.1kHz) DEMO.rar (~16kB)
Mirror 1
Mirror 2
-- 3 files included (2 pictures and the filter .pat file)
NOTE: Filename may become changed by the file service providers system.

Max/MSP 4.6.2 Runtime enviroment for PC/MAC (~4.5MB/9.1MB)

Setting it up (Windows):
- connect your turntable output through some flat pre-amp (no RIAA stage in signal path) into PC through soundcard line input(s)
- connect your output device (amp/active speakers/headphones) into soundcard output(s)
- install the Max/MSP runtime enviroment
- extract the "RIAA Filter (for 44.1kHz) DEMO.rar" to your harddisk
Start the RIAA Filter program either by
- starting the runtime enviroment and Open the "RIAA Filter (for 44.1kHz).pat" or
- double-clicking the "RIAA Filter (for 44.1kHz).pat" (through Windows Explorer -> .pat extention should be associated to Max/MSP runtime then)

In "RIAA Filter (for 44.1kHz)" screen (important):
- set I/O devices; ASIO recommended (if no sound, remember check settings in your mixer software)
- adjust the Subsonic filter by dragging w/ mouse (Hz = 25Hz and Q = 0.71 are good to start from) (see below)
- adjust Gain to somewhere near the 0dB mark (128)
- press the Play/Stop button to enable the playback through filter

NOTE: If you can hear audio when Play/Stop is set "OFF" (there should be total silence) then you need to set something in your mixer software (maybe monitoring OFF, mute something, etc.) otherwise the unfiltered signal is summed into playback --> brighten sound.

Some notes:

Subsonic filter:
It's low order highpass filter so the cut is not very sharp/steep ... you can use 25-30Hz as cutoff frequency w/o loosing much from above the 20Hz frequencies.

RIAA filter:
You see the RIAA de-emphasis curve for this filter as a background image for Filter screen. The original filter coefficients (15 decimal accuracy) gives quite accurate de-emphasis curve (error:

jiiteepee
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Joined: Mar 21 2007 - 6:14am
Re: Phono RIAA EQ filter (evaluation version available)

Hmm... no feedback yet ?

As an addon:

As mentioned, this filter is for 44.1kHz samplerate/data only. What it means is that the mathematical model is matched for amount of this much samples per second (sample accurate processing). Biquad method used in this filter uses three samples to get the new output value calculated (current sample and two previous samples). What happens if you set samplerate to 48kHz, as for an example, ... samples becomes processed wrong --> quality becomes bad.

BTW, as I think this is quite good resulting method for RIAA EQ reproduction, if Stereophile 'testing grew' has not tested equal method yet and is interested to test this filter in action and maybe even compare against your ordinary reference phono pre-amp system (I suppose you have some HQ soundcards there (and maybe using ordinary card as well (SoundBalaster X-Fi, onboard sound)), I could e-mail you the VST plug-in version as a plain RIAA stage only (no additional filters included, only the output level control). This VST version is based on biquad method too, it has four filters (44.1, 48, 88.2 and 96kHz) and it selects the filter automatically by the host software samplerate settings. So, practically, it is a fully working 'RIAA stage' already now.

With certain VST host software, it's possible to record (rip) the LP so that the resulting audio file is processed already ... so, it's not for playback only as the evaluation version is.

jiitee

jiiteepee
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Joined: Mar 21 2007 - 6:14am
Re: Phono RIAA EQ filter (evaluation version available)

I have now improved the VST version a bit . Changed from biquad to 3rd/4th order filters. Some specs from calculations:

Maximum 'curve' error (0 Hz - 20kHz): 0.0005780dB (44.1kHz) - 0.0000046dB (96kHz)
Maximum Phase error (0Hz - 20kHz): ~+/- 21

jiiteepee
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Joined: Mar 21 2007 - 6:14am
Re: Phono RIAA EQ filter (evaluation version available)

No feedback/results yet??

Allright, maybe it is/was too hard to use or too limited to get your attention so, ... I prepared another evaluation version ... now it's fixed for 48kHz instead of 44.1kHz, it can be used without preamplifier too (in most cases) and it's possible to record the output to a 16-/24-/32-/32f-bit wav file (though, this needs another plugin being installed, see below).

I also added a "reset to defaults" button so It's possible to get everything working much easier. Subsonic filter is not improved ... it still cuts only 6dB/oct instead of 'required' 36dB/oct.

'bout recording the output:
You need to install Voxengo Recorder VST plugin into the same directory where to this RIAA Filter is placed to, to get the recorder working. Actually, you could use any plugin but it needs to be renamed equally to the voxengo recorder .dll. Set the "MME Device" to "Sound Mapper" .. otherwise you may hear some unwanted noises (those are not added into recorded file). Set the "Output To " -> "File". Name the file before recording. Set the bit-depth.

Here are links for the new version.
RIAA Filter (optimized for 48kHz) DEMO.rar
Mirror 1
Mirror 2

Hmm... still waiting some feedback/comments ...

jiitee

Jeff Wong
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Joined: Sep 6 2005 - 3:28am
Re: Phono RIAA EQ filter (evaluation version available)

Will this work with Win2K or only XP? My PC is nowhere near my turntable, so, it is unlikely I'll be able to check this out, unless I set up some old less than high-end gear near the computer... I'm a bit reluctant to use the old cartridge and stylus on any records.

jiiteepee
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Joined: Mar 21 2007 - 6:14am
Re: Phono RIAA EQ filter (evaluation version available)

Everything should work well under w2k too but, I didn't get the Max/MSP Runtime installed for w2k. I know some has got XP only software installed/working w/ w2k even I have not managed to do so ... so you need to try if it's possible in your system. It's maybe just the installer that prevents installation for other than XP.

jiitee

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