Recording from tape, speed varies

Using Audacity 2.0.2, on Windows 7 x64 SP1.

I have several 1/4-inch audio tapes on 3-inch reels, recorded on an unknown portable recorder from 1971. Initial recording in Audacity needed about 30 per cent speed increase, but the speed slows down at the end of the 6-minute recording.

I’m using an Akai X-100D reel-to-reel tape deck, new in 1966 and borrowed from a family member. I’m recording from the tape deck using a 3.5mm mini plug, adapted from RCA plugs, which are adapted from 1/4-inch phono plugs.

Is there any way to use Audacity to fix the varying speed?

These are recently discovered recordings of my Grandfather, who died in 1984, and I’d really like to figure out a way to recover them. The tapes were audio letters from him to my parents, who were in Germany at the time, and who have both passed away.

Don Strack

What I would try first is rewinding the tapes from end-to-end a couple of times first before playing them - this is done to even out the tension.

And I would clean the transport mech. of the tape player: the capstan and the rubber pinch-wheel (do not use alcohol or solvent on the rubber pinch-wheel). These often get crudded up with oxide deposits shed from tapes over the years.

Does that fix the varying speed problem?


I had previously cleaned the transport mechanism. Other tapes play at normal speed, although I don’t have a pre-recorded tape from a known source to test the three speeds offered on the Akai tape deck.

It just occurred to me that the tape recorder may have been running progressively slower due to failing batteries.

I can fix the initial speed by using the “Change Speed” drop down in Audacity, but the recording gets slower as it plays.


The “Sliding Time Scale / Pitch Shift” effect can progressively speed up the audio, but note:

  1. It will be very difficult to bring the speed to exactly where it should be
  2. This effect is slow.
  3. Waxcylinder’s suggestion (“rewinding the tapes from end-to-end a couple of times first before playing them - this is done to even out the tension”) and re-recording may be a more successful option.

Thanks for the help. I’ll make note of the need to rewind the tapes back and forth, since there are eight tapes to be recorded. As a test of the tape deck’s current speed capability, a random sample of several 7-inch reels have been tested, and they all play at normal speed. So, it’s the 3-inch reels.

As some additional background, my brother called to ask about the progress. During the conversation, he recalled that the hardware used to record the 3-inch reels was two identical battery-powered portable recorders, each with a mini-plug microphone. This was back in 1970-1971, and our Dad purchased them as a pair in Germany and sent one to our Grandfather, so that they could exchange audio letters. Apparently, the recorders nearly drained the D-size batteries each time a 3-inch tape was recorded, so my assumption about speed variation due to low power was spot-on. I’ll try to find a fix that varies the speed of the Akai tape deck.

Since neither the problem nor the solution is with Audacity, I’ll close this topic.

Thanks for the help. During the past day or so, out of necessity, I’ve learned a lot about Audacity. I’ve used it a lot to record cassettes and vinyl albums, and to capture streaming audio from the web. Great program.


It is worth trying Steve’s suggestion:

But note his caveats (at least it works properly now - it was a bit buggy in the previous release).