If you're experiencing pitch or warble artifacts on some tracks with Pi, there are several things worth looking into:
1. Gain Staging.
Preferably, Pi should be used on a post-fader insert. This way Pi will receive the actual level of the channel in the mix. Unfortunately, some DAW's don't have post-fader inserts. To overcome this limitation, we’ve included CHNL GAIN in Pi to allow setting the average gain for the channel.
Pitch artifacts could happen if low end-heavy instruments are too significant in the levels Pi “sees” which in turn impact softer or lighter instruments by pulling their phase towards the heavier instruments.
If for example, the Bass Drum channel in your mix is set to -15dB, When inserted Pre-fader, Pi ‘sees’ the Bass Drum information coming in at 0 dB. In this case, the Bass Drum is influencing Pi’s phase rotation 15dB stronger than its actual weight in the mix. This will impact other tracks in the mix negatively and may cause artifacts. To improve this, dial the Bass Drum’s Gain in Pi down by 15dB and set its mixer fader to unity gain.
It’s okay to lower or increase the Bass Drum using the mixer fader, just try to avoid cases where there’s such a big difference between the track’s place in the mix and the gain Pi receives.
2. channel Weight.
Increase the channel weight parameter on the offended channel while listening to the entire mix until the artifacts are no longer audible.
3. Group the offended tracks.
Another option is to group the tracks with the pitch/warble artifact in Pi and set the group mode to ‘PL’ (Phase Lock) - This will optimize the phase relationships of the channels within the group and with the mix while keeping the tracks within the group phase-locked.
When Pi is in Phase Lock mode, it won't rotate the phase on the individual channels in the group but rather rotate them as one against the mix.
4. Choose what goes into 'Pi'.
The most significant and noticeable interactions and cancellations in a mix usually occur in the low/low-mid frequency range. Using Pi on higher-range instruments (like Tamborine or Shakers) won't always be beneficial and may influence the tracks without a significant improvement to the mix.
In conclusion, baking is both science and art. So is Pi.