Is there a tutorial on how to correct for the EQ differences between 15 ips and 30 ips in audacity?

I’m digitizing a 30 ips multi-track 4 channel 1/4" tape using TEAC 3340 at 15 ips and doubling the speed in audacity. I was told to correct for EQ differences. Is there a tutorial on how to do this?

I don’t think you’ll find a tutorial or “preset”. You’ll have to research the NAB or IEC curves.

Or, if it doesn’t “sound right” maybe you can just tweak it by-ear. It wouldn’t be unusual to “re-master” the recordings when they are digitized anyway and if wouldn’t make sense to get the tape EQ perfect only to re-EQ by-ear during remastering.

I assume you know what tape EQ is… I don’t know the exact details but the treble is boosted during recording (and maybe the bass is cut) and the opposite is done during playback. It’s similar to RIAA EQ for vinyl records, except the RIAA curve is widely published.

So there are two issues (I think). I believe the curves are different for different speeds so if you can find the two curves you can figure-out the differences and make the correction. That shouldn’t be too difficult if you can find the curves.

The speed (and pitch) change is trickier… If the highs were boosted above 3kHz during recording and you play-back at half-speed, 3kHz is shifted-down to 1.5kHz during playback so the sounds that should be 3kHz (and will be 3kHz after speed correction) are not touched.

…Another big issue could be if the tapes have Dolby noise reduction. I’m pretty sure there is no official software digital Dolby-A decoder (and pro 30IPS tapes would be Dolby-A). Somebody made an unofficial version but you’d have to search for it. And in order to work properly it has to be calibrated (to the analog tape). That requires a Dolby calibration tape or a calibration tone on the tape. Without that there is no way to find the correct digital calibration level.

The free demo version of this AutoEQ plugin will give you an idea of what adjustments to make