Flanger problem when double-tracking Vocals

Flanger effect is produced by having two identical copies of the sound with one copy delayed no more than 20ms.

When you double-track vocals, in a way you are prone to produce the flanger effect when the second take hits within 20ms of the first take. This does not sound nice (unless intended). The voice will sound at times, boxy, flanged or phased. The problem lies in that the singer is probably going for the second take using the same mic, same Mic-pre, same settings on the Mic-pre and same distance from the mic. This all leads to producing a somewhat identical copy of the 1st take… this means, when both tracks are played, you are likely to hear flanging on certain words.

Remember, that parallel compression, even though it uses the same copy of the track, does not exhibit the phaser effect; due to the fact that the heavy compression has changed the harmonics and the wave shape (you are crushing the peaks). So we are not trying here to go this far, but use the same principle of changing the wave shape, so as it does not create an identical shape which could lead to phasing and or flanging.

How to counter that? 

Simply, try not to generate a near identical version of the first one. Here are some tips:

  1. If you are using a compressor in the recording chain, change the setting a bit. For example, if you were applying 3:1, change it to 5:1 but ease it on the threshold.
  2. If your Mic-pre has a gain and output knob, try changing the setting, for example, lower the gain and increase the output to compensate (this works well when your Mic-pre has an output transformer).
  3. Change Microphone or Mic-pre.
  4. Do the second take for doubling the vocal track at a later date, as the vocal quality and energy of the singer would have changed.