Free online VOX to MP3 converter

A legacy voicemail system, telephone recorder, or dictation application may produce a .vox file that ordinary media players and editors cannot open. Converting it to .mp3 makes the recording easier to play, share, edit, and store in a smaller file.

What the VOX format is

VOX usually refers to a raw Dialogic or OKI ADPCM audio file rather than one completely standardized container. Telephone systems, voicemail hardware, dictation software, speech applications, and older recording programs commonly use the .vox extension.

Many VOX files contain no header describing the sample rate, channel count, or codec. Common characteristics are 4-bit Dialogic ADPCM, mono audio, and a sample rate of 6000 Hz or 8000 Hz, but the correct values depend on the creating device or application. Renaming recording.vox to recording.mp3 changes only the filename; it does not decode or convert the audio.

What the MP3 format is

MP3 is a widely supported lossy audio format. Phones, browsers, media players, editing software, and messaging platforms can generally play it without the source application's codec. MP3 files can include ID3 metadata and use selectable bitrate, sample rate, and channel settings.

For speech from a telephone or voicemail system, mono MP3 at 32–64 kbps is usually adequate. Use 96–128 kbps for music or when reducing compression artifacts matters. MP3 cannot restore frequencies or detail that were discarded by the original telephone recording or ADPCM encoding.

How to convert VOX to MP3

Using 101convert.com

1. Open the VOX-to-MP3 converter on 101convert.com. It can be used free without installing software.
2. Upload the .vox file and start the conversion.
3. If source settings are requested, enter the sample rate, channel count, and encoding documented by the original system. Use mono and 8000 Hz only when those settings match the source; do not guess for important recordings.
4. Download the resulting .mp3 file and check its beginning and end for correct speed, pitch, volume, clipping, and missing audio.

Using SoX on a computer

SoX can decode common Dialogic VOX files when the source properties are known. Decode to WAV first, then encode the WAV as MP3 with software that includes an MP3 encoder:

sox -t vox -r 8000 -c 1 input.vox decoded.wav

For a 6 kHz source, replace -r 8000 with -r 6000. The -t vox input type tells SoX to interpret the data as Dialogic ADPCM; -c 1 specifies mono. Then use FFmpeg:

ffmpeg -i decoded.wav -ac 1 -b:a 64k output.mp3

Replace 64k with 32k for smaller speech files or 128k for general audio. SoX builds with direct MP3 output can also write the final file, but the WAV intermediate makes decoding and encoding errors easier to isolate.

Quality and compatibility limits

Incorrect raw-audio settings cause predictable problems. An incorrect sample rate changes playback speed and pitch; the wrong ADPCM variant produces harsh noise, distortion, or silence. If Dialogic settings fail, identify the creating device or application and obtain its documented codec, sample rate, channel count, and any header or byte-order requirements.

Not every file with a .vox extension is Dialogic ADPCM. Some use another codec or a proprietary header, so a generic VOX converter may reject them or produce unusable audio. Desktop tools such as Audacity may also vary in their support for raw Dialogic ADPCM; its raw-data importer should not be treated as a guaranteed VOX decoder.

Keep the original VOX file as the archival copy. Decode it once and create the required MP3 rather than repeatedly converting between lossy formats. Telephone recordings are normally mono; exporting them as stereo increases the file size without adding information.