Foo DSP EqSplit Tips: Improve Mixing with Precise Band SplitsFoo DSP EqSplit is a flexible tool for creating multiband processing chains inside DAWs and hosts that support VST/JS-like plugins (commonly used in Reaper via the JSFX or VST frameworks). By splitting an incoming signal into independent frequency bands you can treat lows, mids, and highs separately—applying different EQ, dynamics, saturation, or spatial processing to each band. This article explains practical tips and workflows for using EqSplit effectively to improve mixes with precise band splitting.
Why use band splitting?
Band splitting gives you surgical control over each part of the spectrum:
- Reduce masking by processing overlapping instruments separately.
- Tailor dynamics per band (e.g., compress lows differently than highs).
- Apply different coloration—tube or tape saturation on mids, gentle harmonic enhancement on highs.
- Simplify automation by addressing frequency-specific issues without affecting the rest of the mix.
Understanding how EqSplit works
EqSplit typically uses a set of crossover filters to divide the signal at chosen frequencies into separate outputs (often low, low-mid, high-mid, high). Common technical details:
- Crossovers can be Linkwitz-Riley, Butterworth, or other designs. Linkwitz-Riley is commonly preferred for minimal phase problems and flat summing.
- Filter slopes (12 dB/octave, 24 dB/octave, etc.) determine how much overlap occurs between adjacent bands. Steeper slopes reduce overlap but can introduce phase artifacts.
- Linear-phase vs. minimum-phase: linear-phase crossovers avoid phase shifts at the cost of latency and potential pre-ringing; minimum-phase is zero-latency and may shift transients.
Tip 1 — Choose crossover points musically, not arbitrarily
Instead of default numbers, choose split points based on instrument roles and problem frequencies:
- Kick fundamentals often live 50–100 Hz → set a low/low-mid split around 80–120 Hz if separating sub from punch.
- Bass harmonics and low-mids sit from ~120–400 Hz → a split near 200–300 Hz can isolate muddiness.
- Presence and body for guitars and vocals often 1–3 kHz → use splits to isolate these for focused processing.
- High-frequency air and sibilance above ~8–12 kHz can be treated separately.
Listen while adjusting. Sweep the crossover point and bypass bands to hear the musical effect.
Tip 2 — Pick appropriate filter types and slopes
- Use Linkwitz-Riley (commonly 24 dB/oct LR24) for smooth summing when you’ll recombine bands later.
- Use steeper slopes (24 dB/oct or higher) when you need clear separation (e.g., sending lows to a sub-processor) but listen for phase smearing.
- If latency or pre-ringing is an issue (live scenarios), prefer minimum-phase filters or compensate latency elsewhere.
Tip 3 — Treat each band with a specific purpose
Define processing goals for each band before adding effects:
- Low band: tighten with compression, remove sub rumble with high-pass if needed, add harmonic sub-saturation to enhance weight.
- Low-mid band: control boxiness and muddiness with subtractive EQ and narrow dynamic control.
- High-mid band: shape presence and intelligibility—gentle boosts can bring vocals forward; surgical cuts tame harsh resonances.
- High band: add air with shelving boosts, gentle exciter or tape-like saturation; apply de-essing if sibilance lives here.
Example chain per band:
- EqSplit → Band EQ → Band Compressor (sidechain or multiband) → Saturation → Recombine
Tip 4 — Use parallel processing with split bands
Instead of destructive inline changes, send split bands to parallel busses for blending:
- Send the low band to a parallel bus for heavy transient shaping or distortion, then blend back to taste.
- Duplicate a band, heavily process one copy (e.g., aggressive compression), and mix it under the original for clarity and weight.
This gives more control and avoids ruining the overall tonality.
Tip 5 — Handle phase and summing carefully
When recombining bands:
- Solo each band and listen for phase cancellation around crossover frequencies. If you hear dips or smearing, try a different crossover type or slope.
- When using other plugins on individual bands that introduce phase shift (analog-modeled EQs, saturators), check the summed result.
- For linear-phase crossovers, compensate or accept latency; align in your host if necessary.
Tip 6 — Use sidechain and dynamic cross-band interactions
EqSplit enables creative dynamic routing:
- Compress the low band with a sidechain triggered by the kick to duck bass energy when the kick hits.
- Make the low-mid band transient-responsive to bring out attack of a guitar only when it crosses a threshold.
- Trigger a band-limited de-esser on the high band with a vocal’s sibilance.
These interactions can reduce masking and make parts sit together better.
Tip 7 — Apply different spatial processing per band
Stereo width and reverb react differently across frequencies:
- Narrow the low band to mono (up to ~120 Hz) to keep low-end focused and compatible with club or mono playback.
- Widen mids and highs slightly with careful mid/side widening for a sense of space, but avoid widening that causes phase issues or collapses in mono.
- Use band-limited reverb: short, small-room reverb on lows; longer, brighter reverb on highs for air.
Tip 8 — Use automation on crossover points and band gains
Automation adds movement and mix clarity:
- Move crossover points dynamically during a track (e.g., tighten lows in verse, open in chorus).
- Automate the gain of a band to emphasize a lead part only in certain sections (boost mids on a vocal for a bridge).
Automated transitions must be smooth—use gradual moves to avoid audible jumps.
Tip 9 — Pay attention to gain staging and leveling per band
Splitting can change perceived loudness:
- Match gains when bypassing and enabling bands to avoid level jumps that bias your ears.
- Use metering per band (RMS/true-peak) to maintain consistent energy and avoid overdriving downstream processors.
Tip 10 — Troubleshooting common issues
- If you hear comb filtering or weird phase artifacts, try a different crossover type (Linkwitz-Riley) or reduce slope steepness.
- If low-end becomes boomy after processing, tighten the low band with transient shaping or a low-frequency shelf cut around 120–250 Hz.
- If highs become brittle, reduce the boost or add gentle harmonic saturation to smooth transients.
Practical example workflow (vocals)
- Insert EqSplit on a vocal bus and split into three bands: low (<200 Hz), mid (200 Hz–3 kHz), high (>3 kHz).
- Low band: high-pass slightly around 50–60 Hz, light compression to control plosives.
- Mid band: surgical cuts at 300–500 Hz to reduce boxiness; gentle 2–3 dB presence boost at 2–4 kHz.
- High band: de-esser or narrow cut for sibilance, subtle airy shelving at 10–12 kHz.
- Add a light parallel saturation on the mid band to enhance presence, then recombine and balance.
Final thoughts
EqSplit is powerful when used with intention: pick musical crossover points, choose filter types that suit the mix, and assign clear processing goals to each band. Use parallel routing, automation, and careful phase checking to maintain a cohesive, natural sound. With practice, band splitting becomes a precise tool to reduce masking, sculpt tone, and improve clarity across complex mixes.
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