Can you believe it? Tape Project is ten years old! Thanks to everyone who has supported us in introducing studio quality tape reproduction to the audiophile community!

Author Topic: Equalization curves  (Read 15463 times)

Offline dyana

  • Newbie
  • *
  • Posts: 1
    • View Profile
Equalization curves
« on: October 01, 2009, 09:40:44 AM »
As a relative newcomer to tape playback, I would like ask a probably dumb question: can anyone give me an insight into the key frequency differences between RIAA equalization and IEC and NAB equalization? Your help would be appreciated.

Offline docb

  • Administrator
  • leader in spreading disinformation
  • *****
  • Posts: 1345
    • View Profile
    • Bottlehead Corp.
Re: Equalization curves
« Reply #1 on: October 01, 2009, 11:40:23 AM »
The upper turnover frequency for NAB is 3150 Hz. The upper turnover frequency for IEC1/CCIR is 4500Hz. So the treble cut comes in a little higher for IEC and an NAB tape played on IEC eq would sound a bit dull on top. Conversely an IEC tape played on NAB eq would be somewhat bright on top.

On the bottom end there is a corner at 50Hz for NAB and theoretically there is no corner for IEC, but there has to be one somewhere or the theoretical IEC eq curve goes to infinity dB at 0Hz. The lower a turnover frequency you choose to get close to this theoretical infinite point at 0Hz, the more gain you sacrifice in a passive IEC eq relative to the NAB setting in the same repro amp. We chose about 17 Hz for the LF roll of the Tube Repro. On the Seduction preamp with it's 10dB lower overall gain we kept the 50Hz corner in the circuit for IEC to conserve as much gain as possible. This can be adjusted down to 25Hz at the sacrifice of 6dB of gain in the midband.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline steveidosound

  • Sr. Member
  • ****
  • Posts: 484
    • View Profile
Re: Equalization curves
« Reply #2 on: October 01, 2009, 01:15:02 PM »
The upper turnover frequency for NAB is 3150 Hz. The upper turnover frequency for IEC1/CCIR is 4500Hz. So the treble cut comes in a little higher for IEC and an NAB tape played on IEC eq would sound a bit dull on top. Conversely an IEC tape played on NAB eq would be somewhat bright on top.

On the bottom end there is a corner at 50Hz for NAB and theoretically there is no corner for IEC, but there has to be one somewhere or the theoretical IEC eq curve goes to infinity dB at 0Hz. The lower a turnover frequency you choose to get close to this theoretical infinite point at 0Hz, the more gain you sacrifice in a passive IEC eq relative to the NAB setting in the same repro amp. We chose about 17 Hz for the LF roll of the Tube Repro. On the Seduction preamp with it's 10dB lower overall gain we kept the 50Hz corner in the circuit for IEC to conserve as much gain as possible. This can be adjusted down to 25Hz at the sacrifice of 6dB of gain in the midband.

So, the RIAA  phono curve has 2122 Hz, 500 Hz and 50 Hz. So the 50 remains the same or is dropped to some lower frequency for IEC, 2122 gets changed to 3150 (NAB) or 4500 (IEC) and what about the 500Hz. Eliminated? How? Does it depend on how it is implemented in the preamp?
Steve Williams

you don't want to know what equipment I listen to...

Offline docb

  • Administrator
  • leader in spreading disinformation
  • *****
  • Posts: 1345
    • View Profile
    • Bottlehead Corp.
Re: Equalization curves
« Reply #3 on: October 01, 2009, 01:26:31 PM »
The shelf at 500Hz in the RIAA curve is not implemented in tape curves. That part of the filter in the RIAA curve is left out of the tape curve. If you look at the conversion we do on a Seduction from RIAA to tape you will see that a .01 cap and .0012 cap in parallel are removed when changing over to NAB or IEC eq.

http://www.bottlehead.com/et/adobespc/Seduction/bottleheadtapeheadpreamp.htm
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline PJ

  • Full Member
  • ***
  • Posts: 31
    • View Profile
Re: Equalization curves
« Reply #4 on: October 01, 2009, 10:45:01 PM »
Perhaps this will help.

RIAA has three corner frequencies. Practical IEC has two. Theoretical IEC has only one.
Paul Joppa
Bottlehead R&D

Offline jcmusic

  • Sr. Member
  • ****
  • Posts: 345
    • View Profile
Re: Equalization curves
« Reply #5 on: October 04, 2009, 09:25:43 AM »
The upper turnover frequency for NAB is 3150 Hz. The upper turnover frequency for IEC1/CCIR is 4500Hz. So the treble cut comes in a little higher for IEC and an NAB tape played on IEC eq would sound a bit dull on top. Conversely an IEC tape played on NAB eq would be somewhat bright on top.

On the bottom end there is a corner at 50Hz for NAB and theoretically there is no corner for IEC, but there has to be one somewhere or the theoretical IEC eq curve goes to infinity dB at 0Hz. The lower a turnover frequency you choose to get close to this theoretical infinite point at 0Hz, the more gain you sacrifice in a passive IEC eq relative to the NAB setting in the same repro amp. We chose about 17 Hz for the LF roll of the Tube Repro. On the Seduction preamp with it's 10dB lower overall gain we kept the 50Hz corner in the circuit for IEC to conserve as much gain as possible. This can be adjusted down to 25Hz at the sacrifice of 6dB of gain in the midband.
Dan,
Please explain to me the advantages of recording in IEC over NAB if there are any? Or vise versa?

Jay
Redpoint Model D TT/Soundsmith Sotto Voce Cartridge Otari MX 5050 BII/BH Tube Repro deHavilland Model 222
 Ah Njoe Tjoeb 4000, Rogue Magnum 99, Korneff 45 SET Amp, Klipsch K-Horns Bass Bins/2" Tractrix Horns 2" BMS Drivers, Vintage Tubes.

Offline Brian C.

  • Full Member
  • ***
  • Posts: 52
    • View Profile
Re: Equalization curves
« Reply #6 on: October 04, 2009, 10:10:00 AM »
Jay, have you read Arian Jansen's article?

http://laocaudiosociety.net/tech/NABtoIEC.pdf

He claims NAB superior for 7.5 ips.


Brian.
Brian Clark, One Inch Studio, London, UK.

Offline ironbut

  • Global Moderator
  • leader in spreading disinformation
  • *****
  • Posts: 2503
  • rs1500>repro amp#1
    • View Profile
Re: Equalization curves
« Reply #7 on: October 04, 2009, 10:58:11 AM »
Hi Jay,

I think from a purist view (which I strongly subscribe to) the less manipulation of the signal the better. In the case of NAB you're eq'ing the bass as well as the treble effectively doubling the number of resistors (in a passive circuit) of an IEC eq circuit. Even the best resistors have some coloration and while this might be insignificant with some lesser music source, I don't doubt that you could perceive their colorations if you A/B'ed different resistors with a TP tape.
Another thing to take into consideration is that this eq'ing is done once in the recording process and again in during playback.

On the other hand, I don't believe that these small differences would be as noticeable when recording a source which has already been thoroughly processed like LP's or CD's. I think that the quality of your phono playback (and lp cleaning before recording) or your DAC is far more significant to the finished recording than the eq that you'll use. The tape that you use will also determine the "character" of your recording a little so experimenting with the available tape types to find the one that you prefer should be done.

If you are planning to do "live" recordings, you'd probably want to eek out every last bit of fidelity you can. But here again, the quality of your mic's, microphone placement, and mic preamps will play a bigger part in the final product.

If you guys haven't noticed it, I'm a big believer in optimizing what I have at hand (or maybe I'm just plain cheap!). And while there may be a few lp's or cd's that might benefit from the use of another eq (other than NAB), I don't think that it's worth the extra trouble.
steve koto
 Sony scd 777es(R. Kern mods)> Vpi Aires>Dynavector XX-2mkll>Bent mu>CAT ultimate>CJ premeir 140>Magnepan 1.6qr(Jensen xover)Headphone Eddie Current Zana Deux>AT ad2000,HD800 ,Metric Halo ULN-2 (battery powered),
 HE Audio Jades

Offline jcmusic

  • Sr. Member
  • ****
  • Posts: 345
    • View Profile
Re: Equalization curves
« Reply #8 on: October 04, 2009, 11:07:42 AM »
Steve,
Correct me if I am wrong, but it sounds like you are saying that IEC has less possible coloration than NAB?

Jay
Redpoint Model D TT/Soundsmith Sotto Voce Cartridge Otari MX 5050 BII/BH Tube Repro deHavilland Model 222
 Ah Njoe Tjoeb 4000, Rogue Magnum 99, Korneff 45 SET Amp, Klipsch K-Horns Bass Bins/2" Tractrix Horns 2" BMS Drivers, Vintage Tubes.

Offline Brian C.

  • Full Member
  • ***
  • Posts: 52
    • View Profile
Re: Equalization curves
« Reply #9 on: October 04, 2009, 11:09:08 AM »
...maybe I'm just plain cheap!

That's a good discipline bro' .


Brian.
Brian Clark, One Inch Studio, London, UK.

Offline ironbut

  • Global Moderator
  • leader in spreading disinformation
  • *****
  • Posts: 2503
  • rs1500>repro amp#1
    • View Profile
Re: Equalization curves
« Reply #10 on: October 04, 2009, 12:31:24 PM »
Steve,
Correct me if I am wrong, but it sounds like you are saying that IEC has less possible coloration than NAB?

Jay

Ultimately yes. How much depends on the particular circuit/filter. There are no perfect filters so less is always better (no filter is best).
 I guess what I'm saying though, is that there are other factors involved in home recording that make those differences a flea on the elephant's butt. IMHO if you don't have the best digital or analog front end feeding the tape machine, the eq you decide to use won't be audible.
steve koto
 Sony scd 777es(R. Kern mods)> Vpi Aires>Dynavector XX-2mkll>Bent mu>CAT ultimate>CJ premeir 140>Magnepan 1.6qr(Jensen xover)Headphone Eddie Current Zana Deux>AT ad2000,HD800 ,Metric Halo ULN-2 (battery powered),
 HE Audio Jades

Offline jcmusic

  • Sr. Member
  • ****
  • Posts: 345
    • View Profile
Re: Equalization curves
« Reply #11 on: October 04, 2009, 12:32:41 PM »
Jay, have you read Arian Jansen's article?

http://laocaudiosociety.net/tech/NABtoIEC.pdf

He claims NAB superior for 7.5 ips.


Brian.
Brian,
I have read the article and maybe I missed it, but I didn' read where he claims NAB is better at 7.5; help me out here!!!

Jay
Redpoint Model D TT/Soundsmith Sotto Voce Cartridge Otari MX 5050 BII/BH Tube Repro deHavilland Model 222
 Ah Njoe Tjoeb 4000, Rogue Magnum 99, Korneff 45 SET Amp, Klipsch K-Horns Bass Bins/2" Tractrix Horns 2" BMS Drivers, Vintage Tubes.

Offline Brian C.

  • Full Member
  • ***
  • Posts: 52
    • View Profile
Re: Equalization curves
« Reply #12 on: October 05, 2009, 06:34:49 AM »
First page, second paragraph, last sentence:

...for 7.5ips NAB equalization is the better choice in combination with modern tape formulas.

However, since the article is about a NAB to IEC filter solely for 15ips, which he states is the speed where IEC is superior to NAB, he does not elaborate.

I'm of the opinion that life is too short to agonize over such gnat's whiskers and I am sure I will enjoy my 7.5ips IEC transcriptions from CD sources. I always get too engrossed in the music to listen forensically but that just me :o)

Brian.

Brian Clark, One Inch Studio, London, UK.

Offline jcmusic

  • Sr. Member
  • ****
  • Posts: 345
    • View Profile
Re: Equalization curves
« Reply #13 on: October 05, 2009, 07:21:44 AM »
Hi Brian,
You are right life is too short for that sorta thing, I will complete my early listing test later today and then decide. So far they are both really close, I will try different tubes today and decide which tube sounds better with each EQ.

jay
Redpoint Model D TT/Soundsmith Sotto Voce Cartridge Otari MX 5050 BII/BH Tube Repro deHavilland Model 222
 Ah Njoe Tjoeb 4000, Rogue Magnum 99, Korneff 45 SET Amp, Klipsch K-Horns Bass Bins/2" Tractrix Horns 2" BMS Drivers, Vintage Tubes.

Offline Brian C.

  • Full Member
  • ***
  • Posts: 52
    • View Profile
Re: Equalization curves
« Reply #14 on: October 05, 2009, 08:18:32 AM »
That's the spirit Jay! The music's the thing. All else is incidental :o)
Tho' the technical stuff can be fun - in moderation ;o)
Brian Clark, One Inch Studio, London, UK.