How Audio Codecs Work
The term "codec" combines "coder" and "decoder," reflecting the two core operations every audio codec performs. During encoding, the codec transforms raw audio (typically PCM samples) into a compressed format by removing redundant or perceptually irrelevant data. During decoding, it reconstructs an audio signal suitable for playback through speakers or further processing.
Lossy vs. Lossless Compression
Lossy codecs (such as MP3, AAC, and Opus) permanently discard audio information deemed inaudible by psychoacoustic models. This yields smaller files and lower bitrates at the cost of some fidelity.
Lossless codecs (such as FLAC and ALAC) reduce file size without discarding any data, enabling bit-perfect reconstruction of the original signal.
Software Codecs vs. Hardware Codec ICs
Audio codec software runs on general-purpose processors and is distributed as libraries, codec packs, or OS-level components. Developers integrate software codecs into applications for streaming, VoIP, and voice AI pipelines.
An audio codec IC (integrated circuit) is a dedicated chip that handles analog-to-digital and digital-to-analog conversion along with compression. These chips communicate with processors over interfaces like I2S (Inter-IC Sound), SPI, or TDM. Audio codec chips are common in smartphones, smart speakers, and embedded voice devices where low power consumption and real-time performance are essential.
Common Audio Codecs List
Opus: Open, low-latency codec widely used in VoIP and real-time communication.
AAC: Standard for streaming and broadcast with broad device support.
MP3: Legacy lossy codec still prevalent for music distribution.
G.711 / G.729: Telephony codecs optimized for narrowband voice.
FLAC: Open-source lossless codec for archival and high-fidelity playback.
Choosing a Codec for Voice AI
Voice AI systems prioritize low latency, speech-frequency fidelity, and minimal computational overhead. Opus and codec variants tuned for speech (like Lyra or Encodec) are increasingly popular because they maintain intelligibility at very low bitrates. On Android and other mobile platforms, codec availability depends on OS version and installed codec software, so developers must verify support or bundle the necessary libraries.