Change audio levels to match on reel to reel digitizing

Hoping someone can troubleshoot this. I am digitizing reel to reels and have noticed the second side levels are always lower. What is the easiest way to increase the levels using Audacity? Thanks.

If this is an auto-reverse machine the tape heads may be dirty or there could be something else wrong with the machine. Maybe just a calibration adjustment.

If it’s not auto-reverse, everything on the machine is the same and it’s the same tape so it has to be something in related to the original recording.

You can use the Amplify or Normalize effects to adjust the volume(s) after digitizing. There’s no harm in doing that. The quieter side probably has a worse signal-to-noise ratio so you’ll boost the noise along with the signal and that will make the noise more noticeable, but that’s it’s no different from turning-up the analog volume.

With digital recording your recording levels are not critical except you should avoid clipping. There is no tape hiss so you don’t have to record “hot” to overcome the noise. With tape you an go occasionally “into the red” where the tape begins to soft-clip. Analog-to-digital converters are hard-limited to 0dB and if you “try” to go over, you’ll get hard-clipping.