The distinction that matters
Almost everything useful about audio formats follows from one division: whether the format discards information.
Lossless formats reproduce the original samples exactly. FLAC and ALAC compress without discarding â like a ZIP archive, the data comes back intact. WAV and AIFF store samples uncompressed. Decoded, all four give you precisely what went in.
Lossy formats â MP3, AAC, Vorbis, Opus â analyse the audio and remove what a psychoacoustic model predicts you will not hear: sounds masked by louder ones nearby, frequencies at the edge of audibility. The discarded data is gone permanently. Modern lossy encoders are very good, and at reasonable bitrates most listeners cannot reliably distinguish the result from the original in blind testing.
Container versus codec
A frequent source of confusion. .m4a is a container, not a codec â it usually holds AAC, but can hold ALAC, which is lossless. .ogg is a container that usually holds Vorbis. The file extension does not always tell you what is inside.
The formats we accept
| Format | Type | Notes |
|---|---|---|
| FLAC | Lossless | Best input. Compressed, exact, open. Roughly half the size of WAV. |
| WAV | Lossless | Uncompressed. Large â around 10 MB per minute at CD quality, which matters against a 50 MB limit. |
| M4A | Usually lossy (AAC) | Apple ecosystem default. Efficient. May contain lossless ALAC. |
| AAC | Lossy | Generally better than MP3 at equal bitrate. |
| OGG | Lossy (Vorbis) | Open format, good quality, less universally supported by hardware. |
| MP3 | Lossy | Universally compatible. Perfectly usable, though not ideal as a source. |
Which to use as input
The ranking is simple: FLAC, then WAV, then anything else.
The reason is not audiophile mystique. Pitch shifting is a mathematical operation performed on the decoded samples. Starting from lossless means the algorithm works on data that has never been through a psychoacoustic model. Starting from a lossy file means it works on data from which information has already been removed, and the encoding artefacts get processed along with the music.
That said, if all you have is an MP3, use the MP3. The difference is real but modest at a shift this small, and a good MP3 source produces a perfectly acceptable result.
The 50 MB practical problem
Our upload limit is 50 MB, and WAV consumes it quickly â about five minutes of CD-quality stereo. FLAC of the same material is typically 25â30 MB. If you have a lossless source that will not fit as WAV, converting it to FLAC first is lossless and usually solves the problem.
Bitrate, briefly
Bitrate is data per second of audio, and for lossy formats it is the main quality control.
- Below 128 kbit/s â artefacts increasingly audible on good equipment.
- 128 kbit/s â acceptable for casual listening; the historical "standard" MP3 rate.
- 192â256 kbit/s â good; most listeners cannot distinguish this from lossless in blind tests.
- 320 kbit/s â maximum for MP3; diminishing returns above 256.
Variable bitrate (VBR) allocates more data to complex passages and less to simple ones, generally giving better quality per megabyte than constant bitrate at the same average.
Our output format
Converted files are returned as stereo MP3 at a variable bitrate averaging around 180 kbit/s, with the original sample rate preserved. That is good enough that most listeners will not distinguish it from the source in normal use. For archival or production work, use a desktop editor such as Audacity and apply a â31.8 cent pitch change yourself so you can keep a lossless result.
Myths worth discarding
"WAV sounds better than FLAC." It does not. FLAC decodes to bit-identical samples. Any perceived difference is expectation, not audio.
"Higher sample rates always sound better." 44.1 kHz already covers the full range of human hearing. Higher rates are useful during production, where processing headroom matters; for playback the benefit is contested at best.
"Converting a low-bitrate MP3 to FLAC improves it." It cannot. You get a large file containing exactly the same degraded audio. Information already discarded does not return.
A short recommendation
Keep your originals in a lossless format if you have the storage â it means you can always redo a conversion later from a clean source. Hand the converter the best version you own. Accept that the returned file is a convenience copy, not an archival master, and keep the original safe.
When you are ready, our 432 Hz converter accepts all six formats above, either as a file upload or a YouTube link.