libspeexdsp

libspeexdsp is a digital signal processing library from Xiph.Org's Speex project that provides real-time audio enhancement features for speech. It focuses on echo cancellation, noise suppression, and automatic gain control to improve intelligibility in VoIP and conferencing applications. While it is designed to be used with the Speex codec, it can be used with other codecs as well.

The library contains two main components: the echo cancellation subsystem (SpeexEchoState) which estimates and cancels near-end echo from captured audio, and the preprocess subsystem (SpeexPreprocessState) providing noise suppression, automatic gain control, and optionally voice activity detection. The API is frame-based and operates on 16-bit PCM samples, making it suitable for real-time processing in streaming and communication scenarios.

libspeexdsp is written in portable C and distributed under a BSD-like license from Xiph.Org. It has been widely adopted in VoIP and multimedia projects and is commonly packaged in major Linux distributions. It is used by various software pipelines, including components of FFmpeg and GStreamer, among others, to provide DSP functionality without relying on heavier or proprietary solutions.

Historically, libspeexdsp originated as part of the Speex project to deliver efficient speech-focused DSP routines, including echo cancellation, noise reduction, and gain control. While newer DSP options exist in related projects, libspeexdsp remains in use in many applications that favor lightweight, open-source DSP components.