Change Speed

I have about 40 7" reel to reel tapes. My recorder was destroyed in a flood. I now want to convert the tapes to digital. A friend offered to loan me his reel to reel player. The problem is his player’s lowest speed is 3 3/4 while many of my tapes were recorded at 1 7/8. Reading some of the forum’s responses I believe the correct method is to use EFFECT > Speed Change. Do I set this up before recording or after recording. Also, can I copy a full tape into my computer and work on it or should I do smaller portions at a time. This will be a long process no matter what, so I would appreciate help on the best steps to follow to try and copy as fast as possible. Space is not a problem since I have a lot of external hard drives of over 200GB each. I have a Windows 7 HP laptop, and an HP Vista desktop. Any assistance would be greatly appreciated.

The sound quality will be quite poor at 1 7/8 so don’t expect miracles :wink:

If you are intending to edit or process the recordings I’d suggest not recording much more than about an hour of audio at a time. If you are simply converting to digital with no other editing (other than correcting the speed) then you will probably be OK doing an entire side of a tape in one go. Either way I’d recommend that you first have a practice on just a short recording.

To change the speed I would suggest that you record with a sample rate of 44100 Hz (which is the Audacity default) and then change the track sample rate to 22050 Hz.
To change the track sample rate, click on the name of the recorded track (by default it will just be “Audio Track”), and from the drop-down menu select "“set Rate > 22050”.

To create a normal audio file (such as a “WAV” file) you need to Export from Audacity (File menu > Export). The sample rate of the exported file is set by the “Project Rate” (lower left corner of the main Audacity window). Leave that at 44100 (the default).

Reading some of the forum’s responses I believe the correct method is to use EFFECT > Speed Change.

Correct! Although it’s done digitally, and you are actually changing the data instead of the speed, it’s essentially the same as changing the speed on a tape player or record player. It usually works perfectly without side-effects, especially when you are slowing-down.

Do I set this up before recording or after recording.

After recording. Like most audio editors, Audacity doesn’t process audio in “real time”. It works on digital audio files, so you have to create the digital file first. The good news is that it will process the audio much faster than real-time.

Also, can I copy a full tape into my computer and work on it or should I do smaller portions at a time.

It’s probably easier to do a full tape. (You might want to experiment with a short selection first.) The only concern I have is that WAV files are limited to 2GB. So, I recommend that you export (save) in FLAC format (lossless compression). And, it would be a good idea to export to FLAC immediately after digitizing/recording, and make a backup of the original “wrong speed” file… just in case… (You select the export format after recording.)

I should mention a couple of “theoretical issues”, that I’m not too worried about because 1-7/8 IPS is limited quality to begin with:

  • At the higher speed, the frequency/pitch will be shifted-up, and the highest frequencies will be shifted above the normal audio range. When you digitize, the audio is limited to half the sample-rate. So, with a sample rate of 44.1kHz (“CD quality”), you will be limited to 22,050Hz. With double tape-speed, any audio above 11,025Hz will be shifted above that limit and lost. If your soundcard supports 96kHz, use that setting. Otherwise, use 48kHz which all soundcards support. Note that at 96kHz, you are “collecting” twice as many samples as 48kHz and the file size will double. After you’ve corrected the speed, you can save-as 44.1 or 48kHz and everything will be fine. (I assume you’ll want to make a CD or other a high-quality archive copy, even if you also want MP3s.)

  • Tape players use [u]NAB Equalization[/u] (similar to RIAA equalization on vinyl records) that boosts the high-frequencies and cuts the low frequencies during recording. Teh EQ curve is not a straight line, so when you play-back at the wrong speed, the inverse playback-equalization doesn’t get applied perfectly. Again that’s not a big deal, since your 1-7/8 recordings are not super high-fidelity to begin with.

This will be a long process no matter what…

Aa double-speed, recording will only take half the time! :wink: And since the speed change in Audacity will go quickly, the whole process will take less time than listening to the tapes at normal speed!

To clarify a few details…

As we are looking at a simple multiple of the original speed (x 0.5), changing the track sample rate (as described in my previous post will do essentially the same thing as the Change Speed effect, but changing the track sample rate is very much quicker to do than using the Change Speed effect.

yes indeed.

The WAV format is limited to 4 GB, (though some (mostly very old) computers or programs may have a file size limit of 2 GB).

With a sample rate of 44100 Hz, the 4 GB file size limit works out at about 6.8 hours for a 16 bit stereo file (CD quality).

I doubt that this will be a problem as the original 1 7/8 ips recording is unlikely to have anything meaningful above about 5 kHz.

In addition to which, a change of track sample rate as I understand it merely pushes the same number of samples forwards or backwards in time, so is lossless in that sense. Change Speed resamples, so will add (interpolate) samples if slowing down or remove them if speeding up, in order to keep the sample rate (number of samples per second) the same. So Change Speed is very slightly lossy because sample amplitudes change.

This is also only theoretical if the audio is not of high quality.