You find an old MP3 album and decide to keep a better-quality archive. The converter offers FLAC, so you select it. The new files are larger and carry a reassuring lossless label. But the conversion has not recovered the audio information discarded when the MP3 was made.
FLAC can preserve the audio it receives without another lossy encoding step. It cannot know the original recording that existed before an earlier lossy conversion. The FLAC project’s FAQ explains its lossless purpose and the distinction between audio data and other file contents. “Lossless” describes the encoding relationship, not a guarantee that the input came from an untouched master.
Give the collection a source field
Consider three hypothetical files: a FLAC made from your own CD, a FLAC purchased from a distributor, and a FLAC converted from a previously owned MP3. Their extensions match, but their histories differ. Record the source you actually know, along with the date and any relevant edition information.
If the source is unknown, write that. A spectrogram, bitrate or file size may offer clues, but none replaces a trustworthy provenance record. Do not promote a guess into “original master” because the file looks technically impressive.
When conversion can still have a purpose
You may need a particular format for an editing workflow or compatible software. Converting an MP3 to a lossless intermediate can avoid adding another lossy generation during that step. It still preserves the decoded MP3 signal, not the missing pre-MP3 information.
For a listening collection, first ask whether conversion solves a real problem. Keeping the existing file with accurate notes may be more useful than creating a larger second copy with a misleading name. If you have a lawful higher-quality source, make a new copy from that source rather than expecting the converter to reconstruct it.
Compare the edition before judging the codec
A different download can contain a different master, running order or edit. If you compare it with the old MP3 and hear a change, the codec may not be the only variable. Match the recording version and playback level as closely as practical, then describe what you heard without assuming the cause.
Keep the old copy until you have checked the new files, tags and track boundaries. The satisfying end of the job is not a folder full of matching extensions. It is a collection in which you know what each copy is, where it came from and which one you intend to play.
AI-generated editorial illustration; not a documentary photograph.