Sometimes one or two bass resonances keep drawing attention to themselves, whatever record you put on. Hybrid IIR + FIR adds a small set of narrow IIR peaking EQ cuts to DecayCore’s normal FIR workflow for those stubborn room modes. It is optional; a well-behaved bass response does not need extra filters just because there is a checkbox available.
In brief
Hybrid mode assigns supported narrow bass cuts to IIR filters and leaves broadband magnitude and phase work to FIR. Deploy both stages together.
What it is
Standard FIR correction distributes correction energy across the entire filter length. For very narrow, high-Q room modes — common in small or acoustically untreated rooms — a long FIR filter may not be the most efficient tool. An IIR biquad peaking filter can resolve a narrow resonance precisely, with no minimum tap-count requirement.
The hybrid approach uses both:
- IIR (Peaking EQ biquads): handle the narrowest, most confident modal peaks in the bass.
- FIR filter: corrects the broadband magnitude and phase behavior after the IIR stage has already addressed the strongest peaks.
How it works
When hybrid IIR is enabled, DecayCore:
- Detects room modes in the configured bass frequency range using confidence and group-delay excess criteria.
- Checks which confirmed modes remain after the bounded FIR magnitude correction.
- Moves the supported FIR cut into a Peaking EQ biquad and compensates that transferred part in the FIR.
- Adds a bounded, uncompensated residual cut only when the remaining mode independently passes the confidence, group-delay, priority, voice-risk, and residual-authority guards.
- Exports the IIR biquad parameters in the CamillaDSP YAML configuration alongside the FIR convolver block.
This keeps the IIR and FIR responsibilities separated while allowing verified residual modes to receive additional narrow-band reduction. The combined IIR cut never exceeds the configured maximum or the supported source-mode height.
When to use
Consider hybrid IIR when:
- one or two narrow room modes in the bass remain clearly audible despite FIR correction
- measurements show high-confidence, high-Q peaks with strong group delay excess
- you are using CamillaDSP and can deploy an IIR filter stage in your pipeline
Be more conservative or leave it disabled when:
- measurements are noisy or uncertain
- the room bass does not show clear narrow modal peaks
- you are deploying to a system that cannot run IIR biquads alongside FIR convolution
Output and CamillaDSP deployment
When hybrid IIR produces biquads, they are added to the exported CamillaDSP YAML configuration as Peaking EQ filter entries alongside the FIR convolver block.
Important: the IIR and FIR must both be active in your CamillaDSP pipeline for the hybrid correction to work as intended. If you load only the FIR WAV without the IIR biquads, the transferred modal correction and any verified residual reduction will be missing.
Verify your CamillaDSP pipeline includes both stages before finalizing the deployment.
Key parameters
| Parameter | Default | Description |
|---|---|---|
enabled |
false |
Enable or disable hybrid IIR preconditioning |
max_filters_per_channel |
3 |
Maximum number of IIR biquad cuts per channel |
min_freq_hz |
20 Hz |
Lowest frequency considered for IIR modal detection |
max_freq_hz |
200 Hz |
Highest frequency considered for IIR modal detection |
min_peak_db |
4.0 dB |
Minimum peak height required to qualify for an IIR cut |
min_q |
3.0 |
Minimum allowed Q for designed biquads |
max_q |
12.0 |
Maximum allowed Q for designed biquads |
max_cut_db |
6.0 dB |
Maximum combined transfer + residual cut depth per biquad |
min_confidence |
0.30 |
Minimum confidence required at the mode frequency |
min_gd_excess_ms |
10.0 ms |
Minimum group delay excess required for mode detection |
min_cut_priority |
0.0 |
Minimum cut priority score required to place a filter |
These parameters are available in the Advanced tab under the hybrid IIR tuning section.