Sounn

How-To Guide

Generating Correction Filters

Once you have a measurement, Sounn can generate correction filters that flatten your room's frequency response and improve time-domain behavior. This guide explains each parameter and helps you create optimal filters.

8 min readLast updated: January 2025

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Filter Generation Overview

Sounn generates hybrid correction filters that combine two technologies:

  • IIR (Infinite Impulse Response): Efficient parametric EQ for broad tonal correction
  • FIR (Finite Impulse Response): Linear-phase correction that addresses time-domain problems like modal ringing

The hybrid approach gives you the efficiency of IIR filters with the phase-correction capabilities of FIR filters.

Diagram showing IIR and FIR filter stages

Sounn's hybrid filter combines IIR efficiency with FIR phase correction

Selecting a Target Curve

The target curve defines what frequency response you want after correction. Sounn includes several built-in curves:

Flat

A ruler-flat response with equal energy at all frequencies. This is technically "accurate" but often sounds thin and bright in a home environment because room reflections naturally add bass energy that your brain expects.

Harman In-Room (Recommended)

Based on extensive listening research by Harman International, this curve features a gentle bass boost and slight treble roll-off. Most listeners prefer this to flat, and it's an excellent starting point.

House Curve

A more aggressive bass boost and treble reduction than Harman. Popular for home theater and listeners who prefer a "warm" sound.

Custom

Create your own target curve by adjusting bass, midrange, and treble tilt. Use this to fine-tune to your personal preference.

Start with Harman

If you're unsure which curve to choose, start with Harman In-Room. It's the result of extensive research into what most listeners prefer, and you can adjust from there.

Correction Parameters

Frequency Range

Sets the lowest and highest frequencies to correct:

  • Low frequency (default 20 Hz): Extending below your speaker's capability is unnecessary and can cause problems
  • High frequency (default 20 kHz): Most people can't hear above 16-18 kHz, and correction above this is rarely beneficial

Maximum Boost

Limits how much the correction will boost frequencies. Default is 6 dB, which is conservative and safe.

  • Conservative (3-6 dB): Safe for all systems, preserves headroom
  • Moderate (6-9 dB): May require volume reduction to avoid clipping
  • Aggressive (9-12 dB): Only for deep nulls with plenty of amplifier headroom

Boost Caution

Excessive boost at bass frequencies can damage speakers or cause amplifier clipping. Start conservative and increase only if needed.

Maximum Cut

Limits how much the correction will reduce frequencies. Default is 20 dB, which handles most room peaks effectively.

Smoothing

Controls how much the measurement is smoothed before generating correction:

  • Light (1/24 octave): More detailed correction, may try to correct speaker-specific features
  • Moderate (1/6 octave): Balanced approach, corrects room problems while preserving speaker character
  • Heavy (1/3 octave): Broad correction only, very safe but may miss narrow room problems

FIR Taps

The length of the FIR filter determines how much time-domain correction is possible:

  • Short (16,384 taps): Lower latency (~170ms), less bass time-correction
  • Medium (32,768 taps): Balanced latency/correction
  • Long (65,536 taps): Maximum bass correction, higher latency (~680ms)

Latency Considerations

For music listening, FIR latency is generally not an issue. For video watching or gaming, use shorter FIR length or Sounn's "Low Latency" mode which disables FIR correction.

Generating the Filter

Step-by-Step

  1. Go to the Correct tab
  2. Select your measurement (or averaged measurement) from the dropdown
  3. Choose your target curve
  4. Adjust parameters if needed (defaults are good starting points)
  5. Click Generate Filter
  6. Wait for generation to complete (typically 5-15 seconds)
  7. Review the predicted corrected response graph

Reviewing Results

After generation, Sounn shows:

  • Original response: Your room's measured frequency response (gray)
  • Target curve: The desired response (dashed line)
  • Predicted corrected: Expected result after correction (colored line)
  • Correction curve: The actual filter being applied (optional view)

Filter generation results showing original, target, and corrected curves

Review the predicted correction before applying

Fine-Tuning Your Correction

Listening First

Before adjusting parameters, listen to the correction with your favorite music. Pay attention to:

  • Bass: Is it tight and controlled, or still boomy?
  • Midrange: Does it sound natural and clear?
  • Treble: Is it detailed without harshness?
  • Overall balance: Does it match your preference?

Common Adjustments

Correction sounds too bright

  • Try Harman or House curve instead of Flat
  • Add slight treble reduction in Custom target
  • Increase smoothing (less aggressive high-frequency correction)

Bass is still boomy

  • Increase Maximum Cut to allow deeper bass reduction
  • Use longer FIR length for more time-domain correction
  • Ensure measurement was taken at actual listening position

Bass sounds thin

  • Increase Maximum Boost (carefully)
  • Check target curve—Flat may be too lean
  • Verify speaker is capable of the bass you want

Sound seems "processed"

  • Increase smoothing
  • Reduce Maximum Boost
  • Try shorter FIR length

A/B Comparison

Use Sounn's bypass toggle (or keyboard shortcut B) to quickly compare corrected and uncorrected sound. This helps identify whether changes are improvements.

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