How to Use the FFmpeg tiltsdr Audio Filter

Spectral tilt alters the overall frequency balance of a sound recording across the audible spectrum, creating a warmer or brighter tonal character by applying a continuous gain slope. This guide explains how to use FFmpeg's tiltsdr filter to apply a spectral tilt to an audio file, covering command-line syntax, key configuration parameters, and practical usage examples.

Basic Syntax

The tiltsdr filter is applied using FFmpeg’s audio filter graph flag (-af). The basic command structure is:

ffmpeg -i input.wav -af "tiltsdr=option1=value1:option2=value2" output.wav

If no parameters are passed, the filter runs using its default parameters, applying standard linear spectral attenuation or boost depending on the input configuration.

Key Filter Parameters

The tiltsdr filter accepts parameters that dictate how and where the spectral slope is applied across the frequency range:

  • tilt / t: Sets the slope of the spectral tilt in decibels (typically per octave or across the entire frequency range). Positive values tilt the spectrum upward (boosting high frequencies and reducing low frequencies), while negative values tilt downward (boosting lows and attenuating highs).
  • frequency / f: Defines the pivot or center frequency in Hertz (Hz). Frequencies above this point are boosted or cut in opposition to frequencies below this point. The default is typically set to the acoustic midrange, such as 1000 Hz.
  • gain / g: Sets an overall gain offset applied across the processed output to prevent clipping caused by excessive high-frequency or low-frequency boosts.

Practical Examples

1. Brightening Dark Audio

To lift the high frequencies and simultaneously roll off heavy low end, apply a positive tilt value with a pivot around 1000 Hz:

ffmpeg -i input.mp3 -af "tiltsdr=tilt=2.0:frequency=1000" -c:a pcm_s16le output.wav

2. Creating a Warmer, Darker Sound

To dampen harsh high frequencies and add warmth across the lower registers, apply a negative tilt value:

ffmpeg -i input.flac -af "tiltsdr=tilt=-1.5:frequency=1000" output.flac

3. Preventing Digital Clipping with Gain Adjustment

Significant upward tilts can push peak signals beyond 0 dBFS. Incorporate the gain parameter to compensate for high-end boost:

ffmpeg -i voice.wav -af "tiltsdr=tilt=3.0:frequency=1500:gain=-3.0" voice_tilted.wav

Integrating with Video Files

If you are modifying audio within a video container without re-encoding the video track, combine the filter with video stream copying:

ffmpeg -i input.mp4 -c:v copy -af "tiltsdr=tilt=1.0:frequency=1000" -c:a aac -b:a 192k output.mp4

This updates the spectral profile of the audio track while preserving the original video quality and saving processing time.