Check out the new Tape Project website at tapeproject.com, now with online ordering. Inventory is updated every week, so stop by often to see what we have in stock.

Author Topic: 30ips EQ  (Read 4682 times)

Offline stellavox

  • Full Member
  • ***
  • Posts: 234
    • View Profile
30ips EQ
« on: January 17, 2013, 07:00:43 AM »
I'm doing some "research" on 30ips and am ordering a Calibration Tape from MRL (with other speed sweeps to save money).  Looking over their excellent material, it appears that the time constants for 30ips AES EQ (also called IEC2) are HALF those for 15ips IEC (more accurately IEC1; the EQ that the Tape Project uses).  The info also indicates that if you have a frequency sweep recorded at one of those two speeds/EQ's, it will play "correctly" at the other speed/EQ, and visa versa (of course the reproduced frequencies are all shifted "up" or "down" by a factor of two depending on which way you go).  Important thing here for me here is that the playback equalization circuitry and components can be IDENTICAL. Have I got this right?

THANKS

Charles     

Offline docb

  • Administrator
  • leader in spreading disinformation
  • *****
  • Posts: 1345
    • View Profile
    • Bottlehead Corp.
Re: 30ips EQ
« Reply #1 on: January 17, 2013, 07:05:54 PM »
Hi Charlie,

Yeah the HF time constants are 70uS for IEC 7.5ips, 35uS for IEC 15 ips (aka IEC1/CCIR) and 17.5uS for AES 30ips. However IEC2 is actually another name for NAB eq, not AES. HF time constant for NAB is 50uS. And of course NAB also has a LF time constant of 3180uS, similar to the RIAA curve for LP playback. To further complicate things you can't just skip having a LF time constant for the first three eqs, that is to say your repro amp's frequency response can't really go to infinity at 0 Hz. So you have to pick a LF time constant for those eqs that won't interfere with the pre eq of the music signal but still allow you the midband gain you desire. We use something around 9100uS for the LF time constant for IEC1, IIRC.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project