Reference

Speex (.spx)

Speex (.spx) is an open, lossy audio codec designed specifically for speech — voice chat, VoIP, and voice memos — rather than music. It produces very small files at low bitrates but is now largely superseded by Opus, which handles both speech and music better.

Files & formatsGeneral

Speex (.spx)

Also known as: Speex, .spx file, spx audio

Open, lossy codec optimized for speech
Tiny files at low bitrates
Largely replaced by Opus

Built for voice

Speex is a free, open codec tuned for the human voice. By optimizing for speech instead of full-range music, it keeps voice recordings small and intelligible at low bitrates, which made it popular for early VoIP, podcasts, and voice messaging.

It is a lossy format, so it discards data that does not matter much for speech. On music it sounds noticeably worse than general-purpose codecs, because it was never designed for it.

Speex today and converting it

Speex is now considered legacy: its successor Opus covers the same speech use cases and also handles music, so new projects use Opus instead. You will still find .spx files in older voice archives and recordings.

VLC and similar players open .spx. For wider compatibility, convert it to MP3 or AAC; since the source is already lossy speech, keep expectations modest about quality gains.

Related terms

Keep reading the reference.

Files & formatsOpusOpus is a modern, lossy audio format built for high quality at low bitrates. It sounds clearer than MP3 or AAC at the same file size, which is why messaging apps and streaming use it for voice notes and music. It is not lossless, so some original data is discarded.General Files & formatsOggOgg is a free, open container format that wraps compressed audio — most often Vorbis or Opus. The `.ogg` extension tells you the wrapper, not the exact codec inside, so two Ogg files can hold quite different audio. The contents are usually lossy, so files stay small.General Files & formatsAACAAC (Advanced Audio Coding) is a lossy audio format designed as the successor to MP3, delivering better sound at the same file size. It is the default for Apple Music, iTunes, and YouTube, and is what iPhones use for recorded audio.General Files & formatsMP3MP3 is a lossy audio format that shrinks music files by discarding sound details most people cannot hear. It is the most universally compatible audio format, though newer codecs like AAC achieve similar quality in smaller files.General

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