As for MXR Pitch Transposer effects, the H910 H949 will get you close. The A & B sides (optional) are set to identical values. You did say “without glitch or artifacts”, so I left it at MODERN.
You may prefer an earlier Harmonizer model (TYPE). It’s still going to get harsh, as the progressive octaves slam into the ceiling. Adjust MIX and/or FEEDBACK (A/B), or maybe some downstream EQ.
For some good, clean fun, map an expression pedal to PITCH A & B: Heel to 2.000; Toe to 0.500. Tape stop slowdown & acceleration effects. The REPEAT switch captures some glitchiness. Releasing the switch recycles it all through the FEEDBACK loop(s).
