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Old 27th April 2017, 04:00 PM   #421
scott wurcer is offline scott wurcer  United States
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Originally Posted by mediatechnology View Post
Thanks Scott. Other vst plugins, including Olaf's do work on that machine. Only the jiitepee vst seem to break on that particular machine. Not sure why yet. It writes an empty file when rendered.

Has anyone posted a ready-to-use RIAA.ny file?

This looks to be an interesting resource for alternative curves: Playback equalization for 78 rpm shellacs and early 33? LPs - Audacity Wiki
My Linear Audio article had all the historical EQ's in an appendix. The Nyquist thing is a one liner, biquad s (the selection) and the 6 coefficients. Audacity FIR's are linear phase only I don't have the energy to write plug-ins for other SDK's but offer the numerical answers to anyone who wants to.
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Last edited by scott wurcer; 27th April 2017 at 04:18 PM.
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Old 27th April 2017, 06:21 PM   #422
mediatechnology is offline mediatechnology  United States
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Thanks Scott. I think I found what I need here: https://linearaudio.net/sites/linear...ble%20a-1.xlsx and here: https://linearaudio.net/sites/linear...01b%20web.docx

Prior to finding the LA links I visited Wayne Stegall's site Website of Wayne Stegall - Digital Phono Equalization and used riaaiir to produce a Nyquist file. I modified his original 96 kHz example to add 20 dB gain using riaaiir.exe I ticked the legacy version 3 syntax box in Audacity in the Nyquist prompt box. Not sure how accurate this is but it sounds OK:

Quote:
(biquad-m s 1.315951e-001 -1.273543e-001 0.000000e+000 1.000000e+000 -1.867054e+000 8.674785e-001)
The .ny file is here: http://proaudiodesignforum.com/code/...K_20dB_Gain.ny

Last edited by mediatechnology; 27th April 2017 at 06:34 PM. Reason: Added link to test Nyquist file
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Old 28th April 2017, 12:38 AM   #423
mediatechnology is offline mediatechnology  United States
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I just ran some Audio Diffmaker comparisons between analog RIAA EQ, two different IIR Biquad plugins and Cool Edit's FIR.

I used the first 60 seconds of Supertramp's "Logical Song."

One pass was recorded RAW (flat) at 96 kHz a second pass recorded with analog RIAA EQ also at 96 kHz SR.

I then applied RIAA EQ in DSP using Nyquist and .vst in Audacity and used Cool Edit for an FIR example. All the files (32B float) were then normalized to -2 dB. Listening to the files I noticed the FIR EQ sounded different from the rest. (No surprise.)

I then had to convert all of them to 16B files for Diffmaker.

I used the analog EQ'd version as the reference and had Audio Diffmaker compare the Stegall Biquad in Nyquist, the Matthes RIAA vst plugin and finally Cool Edit's FIR.

Analog to either IIR plugin yielded a correlation depth of about 14 dB. (Diffmaker complained about a 0.25 ppm SR error so the depth likely could be higher.) The difference file was some timing error and high top end but nothing odd-sounding.

Analog RIAA EQ compared to Cool Edit's FIR RIAA provided only about a 5 dB correlation depth. As expected the difference file sounded weird.

I then decided to compare the two IIR filters to each other. The null depth was over 60 dB. (And since they were the same pass the SR error was virtually 0.)

My conclusion is that both Wayne Stegall's Nyquist coefficients and Olaf Matthes' vst plugins, both IIR, produce virtually identical results at 96 kHz that are very close to analog RIAA EQ. I can't complain about the sound of any of them.

Cool Edit's FIR just sounds odd in comparison.

YMMV.
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Old 28th April 2017, 01:30 AM   #424
scott wurcer is offline scott wurcer  United States
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Originally Posted by mediatechnology View Post
I can't complain about the sound of any of them.

Cool Edit's FIR just sounds odd in comparison.

YMMV.
You can also generate the impulse response of any of them in Cool Edit and compare to an exact computed impulse response. I doubt you could ever build an analog RIAA to get a very deep null, the problem using diffmaker is that you have no "right" answer as a reference..

The FIR technique works fine in a convolver tool like foobar's foo-convolve or BruteFIR but you need a lot more coefficients than I remember seeing in the Cool Edit example. What I saw was a very undersampled impulse response that would have to be interpolated up to the FFT size used in the filter. I forgot the exact number at 96K but it's around 56 msec of samples for a minimum phase FIR that is micro-dB's accurate.

BTW FFT convolution and literal convolution give exactly the same answer with some trivial bookkeeping to account for the circular nature of the FFT. This can be tested down to the numerical resolution of your processor. I have the file as a short .wav if you want it.
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Last edited by scott wurcer; 28th April 2017 at 01:55 AM.
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Old 28th April 2017, 02:44 AM   #425
mediatechnology is offline mediatechnology  United States
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I doubt you could ever build an analog RIAA to get a very deep null, the problem using diffmaker is that you have no "right" answer as a reference..
True.

I was surprised the null was as deep as it was (14 dB) considering that the reference file (analog) and the RAW file were recorded in two different takes. The time base error of the turntable can be heard and you can hear Diffmaker sliding them in and out of deep null. When it's properly nulled it seems deeper. The null shouldn't be varying over time. I'll compress the Diff'd file into an mp3 and post it later.

When I compared Cool Edit's FIR to the vst plugin the correlation depth was only about 4 dB. Cool Edit's EQ far less accurate than the 1% tolerance analog RIAA.

I need to find a way to record the flat RAW file and the analog EQ'd at the same time to get a fair analog vs. DSP comparison. I don't have a vst version of Audacity and need to figure out how to route it to multitrack record. I may just route one A/D into Audacity and another A/D into Cool Edit and roll both at the same time.

What I did learn is that the three RIAAs - analog, Matthes' vst and Steagell - all sound close enough to each other to be considered useable. Cool Edit's FIR is just not phase-accurate and odd-sounding.

Last edited by mediatechnology; 28th April 2017 at 02:50 AM.
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Old 28th April 2017, 08:27 AM   #426
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by mediatechnology View Post
I need to find a way to record the flat RAW file and the analog EQ'd at the same time to get a fair analog vs. DSP comparison.
If you have an MC cartridge and a flat step-up device (either a transformer or a flat pre-preamplifier), it comes natural to do this:
Use the same output channel of the step-up device to feed in parallel :
(1) the R input of your analog RIAA preamplifier and
(2) the L input of your sound card
The R Output of your analog RIAA preamplifier will be connected to the R Input of your sound card.
The stereo recording you will perform will be L channel flat (to be DSP processed), R channel analog RIAA.
Source material will be one and the same and this is very important.

Another option I have also tried with both MC and MMs is
Use a mono (lateral) record, read it with a stereo cartridge. Use the output of both coils.
One coil of the cart to a flat preamplifier, it’s output to “L In” of the sound card.
The other coil of the cart to an analog RIAA preamplifier, it’s output to “R In” of the sound card.
Even if you cater for equal loading of the two coils, this method is inferior to the first because
a. Ticks and pops are not exactly the same at the output of the two coils and you can do nothing about it.
b. There is a small time difference between the two recordings which you have to adjust. My notes say it is anything between 0.02ms and 0.09ms. Your timing pivot point will be some well defined impulse-like scratches, the smaller are more reliable to use.

Thank you for the good work you have done and made it public.

George
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Old 28th April 2017, 05:38 PM   #427
scott wurcer is offline scott wurcer  United States
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If you have an MC cartridge and a flat step-up device (either a transformer or a flat pre-preamplifier), it comes natural to do this:
George,

For flat recording I agree with Wayne, I found it hard to believe how little gain worked well. What I did is make a battery powered FET follower with some old Toshiba tophat FET's <1nV at low current draw to act as an impedance transformation (thank you mlloyd!) to the mic pre-amps in a Tascam field recorder (DR60d). I could easily see splitting the path after the buffer through flat and RIAA with two recorders (which I have). The timing difference should be far better than sequential plays on TT.
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Old 29th April 2017, 08:50 AM   #428
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Originally Posted by mediatechnology View Post
The time base error of the turntable can be heard and you can hear Diffmaker sliding them in and out of deep null. When it's properly nulled it seems deeper. The null shouldn't be varying over time.
I wonder if its possible to get the original (probably digital) file used for the frequency sweep on the George's HFN&RR Test Record.

Then we can use Prof. Angelo Farina's method to get the complete frequency response ... including the cutter etc ... with the best S/N ratio.

Otherwise, if we are trying to EQ the cartridge and provide RIAA, we are down to choosing between his two long but DIFFERENT pink noise tracks on his two Test Records.

Quote:
Cool Edit's FIR is just not phase-accurate and odd-sounding.
Likely Cool Edit's FIR is Linear Phase like Audacity's. Truly EVIL .. even more EVIL than Scott's FIRs.
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Old 29th April 2017, 09:18 AM   #429
billshurv is online now billshurv  United Kingdom
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Finding an affordable and trustable test record is something that has has concerned me. The new ortofon record may be worth investigating. That or we find someone who can be the calibration standard.

Or we accept that +/-1.5dB is good enough for rock and roll!
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Old 29th April 2017, 01:42 PM   #430
mediatechnology is offline mediatechnology  United States
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Thanks everyone for your posts.

Richard - I do want to clarify that the Wayne Stegall Audacity Nyquist biquad coefficients and Olaf Matthes' vst IIR plugins which also run in Audacity are correct. In fact, the Nyquist RIAA and vst plugins when compared to each other have a correlation null of 60 dB. The point is Audacity is capable of accurate RIAA EQ.

I ran some more tests. At the flip of a switch I can bounce the original RAW playback through the analog RIAA. This adds two conversions to the analog RIAA compare file. In this configuration the analog vs. DSP RIAA have correlation null depths around 10 dB.

I also did simultaneous recording one flat, one with analog EQ. This required two different converters (one USB) with two different footprints. Diffmaker found a 9 ppm error in SR which it had to correct. The analog vs. DSP RIAA has a null depth also around 10 dB.

In both cases the difference sound file revealed three things: (1) An unnulled "blurp" right at the beginning of the file which may affect Diffmaker's null depth measurement. (2) Slight differences in top end which is quite likely converter footprint and (3) minor differences in low end.

The minor difference in low end is not surprising: The DSP version has gain to DC, the Analog version does not have DC gain.

The biquad RIAA available in Audacity using Nyquist or vst are, as a practical matter, as close to analog RIAA as they need to be.

To get a complete picture of the amount of available null, George's mono approach is required. I can use the same converter to acquire both samples. Wire the cart mono. Flat feeds left, right is fed by analog EQ. Only the interchannel A/D differences will affect the difference file.

Other than intellectual curiosity I'm not sure its worth doing because I'm convinced that the two DSP solutions I have for Audacity are probably more accurate than the 1% tolerance analog RIAA network and the Jung/Lipschitz 1% tolerance Inverse RIAA network used to check it.

Sonically the analog and DSP RIAA (if done right) sound virtually identical to me.

EDIT: The difference file comparing the Wayne Stegall Nyquist biquad and analog RIAA (using different convertors) is here: http://www.proaudiodesignforum.com/c...nalog_RIAA.mp3 (320 kbps mp3 approx 1.2 Mb)

The original files were normalized to -2 dB. I edited the uncorrelated portion at the head out. The peak level of the difference file is about -18 dBFS so the two are very close.

Last edited by mediatechnology; 29th April 2017 at 01:57 PM.
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