MB

Multiband Compressor

Frequency-dependent dynamics with phase-coherent crossovers

What It Does

The multiband compressor splits your audio into separate frequency bands (Low, Mid, High, and optionally Air), then applies independent compression to each band. This lets you control harshness in the highs without affecting the bass, or tame boomy lows without squashing the mids.

Think of it like having four separate compressors, each listening to only one part of the frequency spectrum. This is how you de-ess vocals (compress 5-8kHz harshness) or control bass punch (compress lows differently than highs) without the pumping artifacts of full-band compression.

Pro Tip

Click on a band region in the spectrum to open the floating control panel. The purple spectrum overlay shows what frequencies are being compressed in real-time.

When to Use Multiband Compression

  • De-essing: Compress 5-8kHz harsh "s" sounds without dulling the whole vocal
  • Tame harsh mids: Control 2-4kHz resonance or nasal frequencies independently
  • Control bass without affecting highs: Tighten low-end punch while leaving clarity untouched
  • Frequency-specific limiting: Prevent one frequency range from dominating the mix
  • Mastering: Gentle per-band compression for transparent loudness increase

3-Band vs. 4-Band Modes

3-Band Mode (Default)

Splits audio into Low, Mid, and High:

  • Low: Below crossover 1 (default 200 Hz) - Bass, kick, subs
  • Mid: Between crossover 1 and 2 (200 Hz - 2000 Hz) - Vocals, guitars, most instruments
  • High: Above crossover 2 (2000 Hz+) - Cymbals, air, presence

4-Band Mode

Adds an Air band above crossover 3:

  • Low: Below crossover 1 (default 200 Hz)
  • Mid: Between crossover 1 and 2 (200 Hz - 2000 Hz)
  • High: Between crossover 2 and 3 (2000 Hz - 4000 Hz)
  • Air: Above crossover 3 (4000 Hz+) - Ultra-highs, sibilance, breathiness

When to use 4-band: De-essing, mastering, detailed high-frequency control

When to use 3-band: Simpler processing, less CPU, broader strokes

Using the Floating Band Panel

Opening the Panel

Click anywhere on a band region in the spectrum to open the floating control panel for that band. The panel shows:

  • Band name: Low, Mid, High, or Air
  • Bypass button: Power icon to bypass this band
  • Solo/Mute: S (solo) or M (mute) this band
  • GR ring: Purple ring around threshold knob shows gain reduction

Per-Band Controls

Knobs (drag or scroll):

  • Threshold: Where compression starts for this band
  • Ratio: How much compression (1:1 to 20:1)
  • Makeup: Output gain to compensate for compression

Sliders:

  • Attack: 1-200ms (how fast compression starts)
  • Release: 10-1500ms (how fast compression stops)
  • Knee: 0-24 dB (transition smoothness)

Solo and Mute

  • Solo (S): Hear only this band (all others muted). Great for finding problem frequencies.
  • Mute (M): Silence this band. Useful for comparing with/without that frequency range.
  • Bypass: Signal passes through band uncompressed but not muted.

Adjusting Crossover Frequencies

Dragging Crossover Lines

On the multiband canvas, you'll see vertical lines separating bands. Click and drag these lines to adjust crossover frequencies:

  • Crossover 1: Low/Mid split (40-1000 Hz, default 200 Hz)
  • Crossover 2: Mid/High split (200-8000 Hz, default 2000 Hz)
  • Crossover 3: High/Air split (500-16000 Hz, default 4000 Hz, 4-band mode only)

Crossover Presets

Select from the Preset dropdown in the parameter panel:

Preset Crossover 1 Crossover 2 Crossover 3 Use For
Vocal 200 Hz 2000 Hz 8000 Hz Speech, singing - separates body, presence, sibilance
Drums 100 Hz 3000 Hz 8000 Hz Kick (low), snare (mid), cymbals (high)
Full Mix 250 Hz 2500 Hz 6000 Hz Mastering - balanced frequency splits
▶ Gear Head Details: Linkwitz-Riley Crossover Implementation

TabDSP uses Linkwitz-Riley 24dB/oct (LR4) crossovers for phase-coherent band splitting.

What makes LR4 special:

  • Low-pass and high-pass filters both measure -6 dB at the crossover frequency
  • When recombined, they sum to unity (0 dB) with no phase cancellation
  • This ensures the output sounds identical to the input when all bands are set to no compression

Implementation:

  • LR4 = two cascaded 2nd-order Butterworth filters (Q = 0.707 or √2/2)
  • Each crossover has a complementary LP and HP pair
  • LP side feeds the lower band, HP side feeds the upper band
  • Total: 24 dB/octave slope (12 dB from each Butterworth stage)

Behavior at the crossover: Each LR4 crossover splits the signal into a low and a high path with matched 24 dB/octave slopes, so energy rolled off from one band is picked up by its neighbor. At the crossover frequency the two band magnitudes sum back to a flat response, and because the low-pass and high-pass pairs share identical phase behavior across the split, the bands recombine without phase cancellation. The result is that bypassing all band processing reconstructs the original signal transparently — you only hear the bands as separate voices once you start moving their gain, threshold, or ratio.

Crossover smoothing: Crossover frequencies are ramped rather than snapped when you drag them, so sweeping a band boundary stays click-free and the filter pair transitions through intermediate frequencies smoothly.

Comparison to plugins:

  • FabFilter Pro-MB: Also uses LR4 crossovers (default), offers Butterworth as alternative
  • Waves C6: Uses proprietary crossovers (not true LR4)
  • iZotope Ozone Dynamics: LR4 crossovers in multiband mode

Per-Band Compression Controls

Each band has independent compression parameters. Key insight: lower bands need slower attack/release, higher bands can be faster—especially for de-essing.

▶ Per-Band Attack/Release Guidance and Typical Starting Points

Why different bands need different settings:

  • Low band (bass): Slower attack (30-50ms) preserves punch, slower release (300-500ms) prevents pumping
  • Mid band (vocals): Medium attack (10-20ms), medium release (150-250ms) for natural dynamics
  • High band (presence): Faster attack (5-10ms) catches sibilance, medium release (120-200ms)
  • Air band (ultra-highs): Very fast attack (3-5ms) for de-essing, shorter release (80-150ms)

Typical starting points by band:

Band Threshold Ratio Attack Release Purpose
Low -18 dB 3:1 30ms 300ms Control bass without losing punch
Mid -16 dB 2.5:1 10ms 200ms Even out vocal/instrument levels
High -14 dB 2:1 5ms 150ms Gentle presence control
Air -12 dB 4:1 3ms 100ms De-ess harsh sibilance
▶ Gear Head Details: Per-Band RMS Detection

Each band has an independent RMS envelope follower for smooth, musical compression.

RMS detection per band:

  • Short sliding window average, on the order of ten milliseconds
  • Independent detectors per band, with separate tracking for the left and right channels
  • Periodically refreshed so long sessions stay numerically stable

Soft knee per band:

  • Knee range: 0-24 dB (same range as single-band compressor)
  • Signals inside the knee region are compressed by a smoothly increasing amount, so the onset into full ratio is rounded rather than abrupt

Gain reduction metering:

  • Updated at 60fps (sampleRate / 60 interval)
  • Per-band GR sent to UI for mini-meters and floating panel GR ring
  • Max GR across all bands sent for global meter section

Band summing:

  • After compression, bands are summed with makeup gain applied per-band
  • Solo mode: only soloed band output, all others muted
  • Mute mode: muted band is zeroed before summing
  • Bypass mode: band passes through without compression but is still summed

Purple Spectrum Overlay

When multiband is active and "Overlay" is enabled, you'll see a purple spectrum overlay showing post-multiband frequency content.

What It Shows

  • Blue spectrum: Pre-EQ (input)
  • Orange spectrum: Post-EQ (after EQ, before multiband)
  • Purple spectrum: Post-multiband (after multiband compression)

This lets you see exactly how multiband compression is reshaping the frequency balance. If you're compressing highs heavily, the purple overlay will show reduced high-frequency energy compared to orange.

Important Note

The purple overlay only appears when multiband is active (not bypassed). It shows multiband output only, not single-band compressor impact. Single-band compression is visualized on the COMP canvas waveform.

Common Multiband Settings

Starting point recipes for common scenarios.

▶ Show Recipes (De-Essing, Podcast Voice, Mastering Reference, Taming Harsh Mids)

1. De-Essing (4-Band Mode)

Goal: Reduce harsh "s" sounds without dulling the vocal

  • Mode: 4-band
  • Crossover 3: 5000 Hz (separates sibilance from presence)
  • Low/Mid/High bands: Bypassed or very gentle (2:1, high threshold)
  • Air band (5kHz+):
    • Threshold: -14 to -10 dB
    • Ratio: 4:1 to 6:1
    • Attack: 3ms (fast, catch sibilance)
    • Release: 80ms (quick recovery)
    • Knee: 6 dB

2. Podcast Voice (3-Band)

Goal: Even out vocal dynamics across frequency spectrum

  • Mode: 3-band
  • Crossovers: 200 Hz, 2000 Hz (Vocal preset)
  • Low band: Bypass or light compression (prevents mud)
  • Mid band (200-2000 Hz):
    • Threshold: -18 dB
    • Ratio: 4:1
    • Attack: 10ms
    • Release: 200ms
    • Makeup: +6 dB
  • High band (2000Hz+):
    • Threshold: -12 dB
    • Ratio: 3:1
    • Attack: 5ms
    • Release: 120ms

3. Mastering Reference (4-Band)

Goal: Transparent dynamics with frequency balance preservation — for listening enhancement, not export mastering

  • Mode: 4-band
  • Crossovers: 250 Hz, 2500 Hz, 6000 Hz (Full Mix preset)
  • All bands:
    • Very gentle ratios: 2:1 to 2.5:1
    • Soft knees: 20 dB
    • Slow attack: 30-50ms (preserve transients)
    • Smooth release: 300-500ms
    • Threshold: Aim for 2-4 dB max GR per band

4. Taming Harsh Mids

Goal: Reduce 2-4kHz resonance without affecting bass or air

  • Mode: 3-band or 4-band
  • Crossover 2: 1500 Hz, Crossover 3: 5000 Hz
  • Low band: Bypass
  • Mid band (1500-5000 Hz):
    • Threshold: -16 dB
    • Ratio: 3:1
    • Attack: 10ms
    • Release: 150ms
    • Makeup: 0 dB (don't add back what you're removing)
  • High band: Bypass or very gentle

Parameter Reference

Global Parameters

Parameter Range Default Description
Enabled On/Off Off (bypassed) Enable multiband processing
Num Bands 3 or 4 3 Number of frequency bands
Crossover 1 40 to 1000 Hz 200 Hz Low/Mid split frequency
Crossover 2 200 to 8000 Hz 2000 Hz Mid/High split frequency
Crossover 3 500 to 16000 Hz 4000 Hz High/Air split (4-band only)

Per-Band Parameters (All Bands)

Parameter Range Band 0 Default Description
Threshold -60 to 0 dB -18 dB Compression start point
Ratio 1:1 to 20:1 3:1 Compression amount
Knee 0 to 24 dB 12 dB Transition smoothness
Attack 0.001 to 0.5 s 0.03 s (30ms) Compression start speed
Release 0.01 to 2 s 0.3 s (300ms) Compression stop speed
Makeup -24 to +24 dB 0 dB Output gain per band
Solo On/Off Off Hear only this band
Mute On/Off Off Silence this band
Bypass On/Off Off No compression on band