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How the Derumbleizer cancels rumble

Traditional filters blunt the bass to hide rumble. The Derumbleizer takes a completely different approach: it compares the phase of the bass and cancels only the rumble — leaving the music intact.

The simple idea: rumble is out-of-phase bass

When a stylus tracks a record groove:

  • Music is recorded as lateral movement of the groove — left/right movement that produces in-phase bass in both channels.
  • Rumble is mostly vertical movement of the stylus (from the bearing, motor, warps and floor vibration) that produces out-of-phase bass.

There is little or no genuinely out-of-phase bass music — that is the key the Derumbleizer exploits. By separating the bass into the part that is in-phase (music) and the part that is out-of-phase (rumble), it can cancel the rumble and keep the music.

Even a laser-read record in anti-gravity has rumble. The rumble was copied into the record itself when it was mastered on a real turntable. That’s why an active canceller — not just an isolation shelf — is the reliable fix.

The signal path inside the Derumbleizer

  1. Split the bass

    The music in both channels is split into two frequency bands — bass and everything else. Both channels are analyzed together.

  2. Check the phase

    The phase of the bass is checked in both channels. In-phase bass is music and is kept; out-of-phase bass is rumble and is canceled.

  3. Combine, then restore

    The cleaned bass is added back to the “everything else” channels. During this process the bass is made monophonic.

  4. No phase shift

    Because the low-pass and high-pass filter phase shifts are opposite, they cancel on recombination — the signal comes back with the original phase and amplitude.

Block diagram of the Derumbleizer showing bass phase comparison and summation
Simplified block diagram of the Derumbleizer’s bass phase-cancellation stage.

“Don’t panic!” — the bass is monophonic anyway

Making the bass mono is nothing to worry about — bass is monophonic in almost every recording already. Your ears cannot localize bass at low frequencies, and if you use a subwoofer you’re already hearing monophonic bass.

On the rare record with bass in one channel only, the Derumbleizer still removes the rumble and reproduces that bass at the correct volume so it sounds as if it came from one speaker. Nothing important is lost.

The measured result: near-flat gain and phase from 10 Hz to 50 kHz for in-phase (music) signals, with out-of-phase (rumble) signals sharply attenuated below ~100 Hz. See the performance graphs for the untouched measurements.

See the cancellation in action

Review the untouched oscilloscope and measurement graphs.

View Performance Graphs Order the Derumbleizer