Re: [ARSCLIST] Non-RIAA preamp

[Rob Poretti <r.poretti@xxxxxxxxxx>]

Actually, most IIR filters DO introduce phase shifts.  Design criteria
determine how that phase-shift is used to affect the sound quality.  Most
equalizers in WaveLab, Sound Forge, Sadie, etc, are IIR filters that are
emulating "analog-like" equalizers.  Musical sounding equalizers like Neve,
Focusrite, etc. all have phase shift.  A big part of that "analog emulation"
is precisely recapturing the phase shift in certain frequency ranges.
 
FIR equalizers are usually advertised as Linear Phase or FIR filters - and
they are usually purchased separately because there function is slightly
different.  Waves, has at least one.  Cube-Tec has a couple...
 
My mistake on the purpose of the original query - I didn't see that Jeff was
talking about RIAA curves, but now that I re-read his message, I see that he
certainly implies it.  So I can address this directly:
 
The only digital tool that I know of that creates recording emphasis curves
and emulates phase response, is the Cube-Tec Playback-EQ.  This is a VST
plug-in that faithfully reproduces the analog circuits of over 20 different
playback equalizer/transfer curves including RIAA/CCIR, the various NAB and
IEC curves, and a long list of very specific historical transfer functions
used throughout recorded history.  
 
The research was done along with one of the large German universities and
some German broadcasters.  Aside from the presets, you can also create your
own modified versions, in case the original recording EQ was poorly
calibrated.  It will also invert to create the original pre-emphases
functions.
 
Read more here: http://www.cube-tec.com/vpis/restorationvpis/playbackeq.html
 
Of course, you need an AudioCube to run these plug-ins...
 
Cheers!
 
Rob Poretti
Sascom - Toronto
vox.905.825.5373    fax.905.469.1129     cel.905.580.2467
www.sascom.com <http://www.sascom.com/> 

-----Original Message-----
From: Scott D. Smith [mailto:lists@xxxxxxxxxxxxxxxx] 
Sent: September 8, 2006 1:55 PM
To: r.poretti@xxxxxxxxxx
Subject: Re: [ARSCLIST] Non-RIAA preamp


Rob,

I think what Jeff was trying to state was that some digital filter designs
in fact DO NOT introduce phase shift, so that the phase shift introduced by
the analog equalizer used in the cutting lathe would not have a
complementary phase shift when reproduced flat, and then EQ'd for the RIAA
curve in the DAW.

An interesting question. When I have time, I'll have to run some comparison
tests with both methods using test records.

Scott D. Smith


Rob Poretti wrote:


Well it depends on the approach that the digital eq takes for processing...



Digital EQ designers will choose IIR or FIR based on design criteria of the

EQ.  FIR is chosen for phase-linear equalizers.  So... if you're concerned

about this, look for a FIR based tool and you won't have to worry about it.



Cheers!



Rob



  

-----Original Message-----

From: Association for Recorded Sound Discussion List 

[mailto:ARSCLIST@xxxxxxx] On Behalf Of Jeff Brown

Sent: September 8, 2006 11:07 AM

To: ARSCLIST@xxxxxxxxxxxx

Subject: Re: [ARSCLIST] Non-RIAA preamp





There was a lot of support expressed in this thread for 

making flat transfers, then declicking, then applying EQ in software.



But no one addressed the issue of the phase shift correction 

needed to 

compensate

for the phase shift introduced by the original recording EQ.  

With an analog phono preamp the required playback phase 

correction is inherently applied, but I've seen no assurances 

that the digital EQ in the most commonly used software also 

applies the needed phase compensation.



Comments, anyone?