A Second Order Elliptic Equalizer for Vinyl Mastering

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mediatechnology
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Re: A Second Order Elliptic Equalizer for Vinyl Mastering

Post by mediatechnology » Wed Aug 26, 2020 3:02 pm

Kevin -

I finished the EEQ build weeks ago and then got busy building a couple of other boards for customers.

Today I had a chance to connect the EEQ to the output of the PTS.
Connecting the pre-highpass and post-highpass Side outputs to a difference amp allowed me to see and hear warp removal.
I actually used one channel of the PTS' line input and used the PTS monitor output to feed a 'scope and monitor amp.

I didn't do a deep dive looking for a really warped LP - I used a shim under one side of the disc to simulate warp.
It's pretty effective at removing warp and floor vibration transferred into the platter.
I used the 75 Hz highpass setting on the EEQ.

By stopping the platter and tapping on the floor with my foot I can excite the mechanical system and see the resonant frequency of the cart/arm/platter etc.
Its about 14 Hz but highly-damped.

Wayne
https://ka-electronics.com

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KMN
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Re: A Second Order Elliptic Equalizer for Vinyl Mastering

Post by KMN » Thu Aug 27, 2020 1:52 pm

That's pretty cool, man.

After our last conversation, I have wondered, since much of it is undoubtedly subsonic, maybe a good way to use this signal is sending it to a spectral display. Not too many preamp/ADC combos would be able to capture frequencies of interest, probably. but I modded my Flat Phono and tapped off the pre AC coupled side, so I can switch back and forth between AC and DC coupled. According to the manual of my RME ADC it can be put into "DC" mode as well. I think I'm ready for it if I can ever get going on the other half.

I really want to hear it. I have read more about others similar approach. I still think your 2 pole roll off to mimic the recording process sounds "right". May be getting close to time for me to order some fiberglass.

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mediatechnology
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Re: A Second Order Elliptic Equalizer for Vinyl Mastering

Post by mediatechnology » Thu Aug 27, 2020 2:04 pm

I captured it with a Velleman DSO.
The Focusrite 2i2 has a response <<10Hz but I haven't tried it.

I did listen to the warp (without my shim to make it worse) and it has harmonics that are in-band which sound a little like surface noise.
Sounds kinda like a "whump" along with a LF "crackle" which are rotationally-related.
On this particular disc it was once per revolution.

You do hear a little bit of midband audio and bass in the derived low pass response of the warp monitor output.
I don't think this is so much of a lack of filter steepness but more cartridge crosstalk which is typically good in the midband and then worse at each end of the spectrum.
Put another way the cart mechanically converts lateral to vertical.
https://ka-electronics.com

Plandemic Series: "Pland3mic - Indoctornation" https://proaudiodesignforum.com/content ... nation.mp4
Plandemic Series: "Plandemic - Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

CDC: "For 6% of the deaths, COVID-19 was the only cause mentioned. For deaths with conditions or causes in addition to COVID-19, on average, there were 2.6 additional conditions or causes per death." https://www.cdc.gov/nchs/nvss/vsrr/covi ... /index.htm

KMN
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Re: A Second Order Elliptic Equalizer for Vinyl Mastering

Post by KMN » Thu Aug 27, 2020 4:42 pm

mediatechnology wrote:
Thu Aug 27, 2020 2:04 pm
I did listen to the warp (without my shim to make it worse) and it has harmonics that are in-band which sound a little like surface noise.
Sounds kinda like a "whump" along with a LF "crackle" which are rotationally-related.
On this particular disc it was once per revolution.
Nice! This is where the action is. I want to try this.
I don't think this is so much of a lack of filter steepness but more cartridge crosstalk which is typically good in the midband and then worse at each end of the spectrum.
Did you try different corner frequencies?

It might have been here, probably was, or maybe over at VinylEngine. I can't remember, but I saw a post by one of these guys who knows a guy who can say they know a certain studio has used these: x, y, z, a, b, c etc frequencies where they roll off to mono.

I think I want to try that too. ie change filter corner frequency to say 300, 150, 75, 37.5 Hz etc and see what kind of difference , if any, that makes.

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mediatechnology
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Re: A Second Order Elliptic Equalizer for Vinyl Mastering

Post by mediatechnology » Thu Aug 27, 2020 8:02 pm

My options are 75, 150, 300 since those are what have historically been used for cutting based on the Neumann EE-77.
I didn't want to modify a production board.

Mastering facilities are the primary customers for the EEQ.
One of my first clients for the EEQ was Sterling Sound who have over 18,000 album credits.

Almost all vinyl is mono below a certain frequency.
There are exceptions.

I did listen to 150 and 300 but 75 Hz was enough to be effective at warp frequencies.
https://ka-electronics.com

Plandemic Series: "Pland3mic - Indoctornation" https://proaudiodesignforum.com/content ... nation.mp4
Plandemic Series: "Plandemic - Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

CDC: "For 6% of the deaths, COVID-19 was the only cause mentioned. For deaths with conditions or causes in addition to COVID-19, on average, there were 2.6 additional conditions or causes per death." https://www.cdc.gov/nchs/nvss/vsrr/covi ... /index.htm

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