What is lossy compression? It is a way of making a file smaller by permanently removing data that matters little to human hearing or sight. MP3 and AAC do this for sound, JPEG for pictures. The loss cannot be undone, so the smaller file never returns to the original.
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Files up to 2 GB · export to TXT, MD, DOCX, PDF, SRT and VTT · speaker labels and timestamps · about 30 languages
Key facts
- The encoder follows a model of hearing: it drops quiet sounds hidden by louder ones and detail at pitches most people barely notice.
- A lower bitrate removes more data, so the same recording saved at a very low rate sounds thinner than one saved at a moderate rate.
- Every new save in a lossy format removes a little more, which is why copies of copies slowly turn muddy.
- Speech survives lossy compression well at moderate settings, but quiet consonants and distant voices are the first details to blur.
- The file keeps its name and plays normally, so the damage is easy to miss until you listen closely or read an error-filled transcript.
What it looks like
// make a small lossy copy for sharing, keep the WAV as the master
ffmpeg -i interview.wav -c:a libmp3lame -b:a 64k interview.mp3
// compare the two files
ls -l interview.wav interview.mp3
// the MP3 is much smaller, and the removed detail cannot be recovered
More
See the full list of languages, the tools and the glossary.
Frequently asked questions
Can I restore the data that lossy compression removed?
No. The removed detail is gone for good. Converting the file to WAV or FLAC only changes the container and makes the file bigger, not better.
Is MP3 always bad for transcription?
No. A clear voice at a moderate bitrate is usually fine. Trouble starts with very low bitrates, noisy rooms or several rounds of re-saving.
Which is safer for a recording I want to keep, lossy or lossless?
Keep the original recording as it came from the device and make lossy copies from it when needed. Do not edit and re-save the copy.
Why are voice messages lossy?
Chat apps want small files that upload quickly, and speech tolerates the loss well. The price is that very quiet or fast speech is harder to recognise.
What should I send to the Potok bot?
Send the original file when you have it, as audio or as a document, up to 2 GB. A fresh recording is better than a copy saved several times.
Sources
Each source was opened by hand on the date shown. Pages change, so open the source if a detail matters to you.
- Lossy compression (Wikipedia), Wikipedia · checked
- MP3 (Wikipedia), Wikipedia · checked
Try it on your own recording
Send your voice message, audio or video to @potok_now_bot on Telegram and the text comes back in the chat.
Open @potok_now_bot in Telegram