Reel to reel speeds.

I am trying to copy reel to reel tapes into audacity. Audacity already has settings for turntables, such as if you play a 33 1/3 record at 45. My question is, if I play the tape at 7 1/2 IPS, and some of the recording on the tape is 3 3/4 IPS, or 1 7/8 IPS, What percentage do I adjust the speed setting?

It is much better to play the tape at its design speed, not faster. If you must play faster then you will need to set a much higher project rate in Audacity to avoid loss of high frequencies. See

Use your favourite calculator to work out the percentage speed difference to enter in Change Speed. If you prefer, install the attached plugin - see Installing Nyquist plug-ins on Windows.

The plugin appears in Audacity’s Generate Menu. Set Tempo Change as %, then enter to and from values with a space in-between. For example, 7.5 to 3.75 is -50%.

qcalc.ny (6.24 KB)

You will probably still lose high frequencies due to frequency limits of the tape player.

I have a fairly high end reel to reel player, and the frequency response is pretty flat up to 20 kHz, but drops rapidly above 22 kHz. This means that when playing at double speed , frequencies that were originally 12.5 kHz will now be played as 25 kHz and severely attenuated because they are above the design limits of the tape player’s electronics. Similarly, playing a tape at 4x speed will cause frequencies that were originally 6250 Hz to play as 25 kHz and be attenuated in the same way.

Standard tape speeds are multiples of 2:
2 x 1 7/8 = 3 3/4
2 x 3 3/4 = 7 1/2
2 x 7 1/2 = 15
2 x 15 = 30
so to ‘correct’ (slow down) the tape speed you will use multiples of 0.5, 0.25, 0.125 and so on, in the “Speed Multiplier” box. Change Speed and Pitch - Audacity Manual