How to save an audiofile on half speed?

[hdp_rene]

I was asked to digitaze 45 maxell 35-180 analogue tapes. To reduce copytime, I prefer to set the tapedeck speed on 15 inch instead of 7.5 which was used originally. Adjusting JKL in Preferences, Playback & Recording, you can easily slow the playback speed 50%. But how do I save it to a new file with that new speed? I can't seem to find it. Thanks for reading and answering!  Best René 🙂

[SteveG_AudioMasters_ · Accepted solution]

I hope the qualty doesn't matter, because you will lose a lot of HF response using that method. Probably okay for speech, but that's about it.

What you do to save it at the correct speed is open the file, then select Edit>Interpret Sample Rate and set it to half of what you recorded it at. It will now be playing at the correct speed, but with the wrong sample rate. You fix this by going to Edit>Convert Sample Rate and selecting the original sample rate again. This will work fine, but your problem is that if, for instance you made the recordings with a sample rate of 48k then the 'correct' speed version (which is already suffering from losses in the tape machine) will now have an effective sample rate of 24k - which will limit the maximum frequency you will end up with as 12kHz - not so good.

If you are doing a job like this, it's far more common to do it the other way around - half speed replay and double-speed it for the final save. That way you lose nothing.

[hdp_rene]

Hi Steve, Thank you for your answer. You're absolutely right on missing the 12k to 22k audio range. I found the and used the 'strech and pitch' method in Audition, (200% & -12 semitones) which works fine on the speed thing except for the plus 12k range. Doing a copy exercise of 45 tapes of 192 minutes each is  not something to look forward to. These come from a 'tapeclub' in the eighties and are all old collectors recordings from the forties, fifties, sixties and later on from radio, tv or audience made concerts (cassettes). I will do a check and test if it practically hearable on the items.  But thanks again!

[Richard M Knight]

Just a note, I expect the NAB CCIR eq decoding curves will be wrong when playing back at twice the speed.

[hdp_rene]

Hi Richard, Thanks!. Is it possible to make these differences viewable? Btw I'm using a Technics RS 1500 US two track tapedeck for this. It has three bias & equalizer settings.I ordered new pinch rollers to improve the tape accompaniment. The rubber of the original ones feels like stone.

[SteveG_AudioMasters_]

Actually, the NAB EQ is the same for 7.5 and 15ips, so that won't make a difference. If you use IEC/CCIR playback EQ, you'll get about a 1.5dB treble boost - which, all things considered, you aren't going to notice compared to all the other things you've done!

[Richard M Knight]

Although the curves are the same I think they will be and octave out because of the speed difference.