What exactly does bitrate measure?

Bitrate is the amount of data used to describe one second of audio, expressed in kbps (kilobits per second). A 128 kbps MP3 allocates roughly 128 kilobits to every second; a 320 kbps file uses close to two and a half times as much. More data means the encoder can stay closer to the original waveform. Bitrate therefore directly determines both file size and how much audio detail survives.

Is 320 kbps always the best choice?

It is the safest choice for quality, but it is not necessary for every kind of content. For music with a wide frequency range and complex instrumentation, 320 kbps makes sense. For a meeting or lecture captured with a single microphone, however, hearing the difference between 320 and 128 kbps is nearly impossible, while the file grows two and a half times larger. Choosing by content is smarter than blindly picking the maximum.

Should I use constant or variable bitrate?

Variable bitrate (VBR) uses less data during quiet, simple passages and more during dense ones, which generally yields slightly better results at the same average file size. Constant bitrate (CBR) allocates equal data to every second and makes the final size perfectly predictable. VBR is a good default for a music archive; CBR is preferred in technical scenarios such as broadcast streams or telephony systems that require a predictable data rate.

If I re-encode a low-bitrate MP3 at a higher bitrate, does quality improve?

No, it does not. Re-encoding a 128 kbps MP3 at 320 kbps does not recover the discarded audio information; it simply stores the same incomplete audio in a larger file. Worse, re-encoding adds a second round of loss, so the result is usually marginally worse than the original. High bitrates are only meaningful on the first conversion from a lossless source such as WAV or FLAC.

Choosing a Bitrate for WAV to MP3: What 128, 192 and 320 kbps Really Mean

Why bitrate matters so much

When you convert a WAV file to MP3, bitrate is the only real decision you face. Sample rate and bit depth are mostly inherited from the source, but you choose the bitrate, and that choice determines two things at once: how much space the file occupies and how much of the original recording survives.

MP3 is a lossy format. Rather than storing audio as it is, the encoder shrinks the data by discarding components it judges difficult for the human ear to notice. Bitrate is how you tell the encoder how large its budget is. As the budget narrows, the encoder must throw away more; as it widens, it stays closer to the original.

What the numbers mean in practice

A one-hour 44.1 kHz, 16-bit stereo WAV recording is roughly 600 MB. Converted to MP3, that same recording occupies approximately:

96 kbps: around 40 MB
128 kbps: around 55 MB
192 kbps: around 85 MB
256 kbps: around 110 MB
320 kbps: around 140 MB

These figures come from a rough calculation: bitrate × duration. As you can see, there is more than a threefold gap between the lowest and highest options — and on long recordings that difference becomes very noticeable in both storage and upload time.

Which bitrate for which content?

Music

Music is the content type most sensitive to compression, because it contains a wide frequency range and overlapping instruments. Cymbals, the initial transient of drum hits, and high-frequency detail are the first things to break down at low bitrates, usually heard as a metallic or "watery" quality.

256–320 kbps: If you listen through good headphones or speakers, or if this file will live in your library for years, this is the right range.
192 kbps: A reasonable middle ground between size and quality. Sufficient for most people on a phone, in noisy environments, and for everyday listening.
128 kbps and below: Not recommended for music. It saves space, but the difference becomes audible, particularly in the high frequencies.

Speech: podcasts, interviews, lectures, meetings

The human voice occupies a far narrower frequency range than music. Speech recordings therefore hold up surprisingly well at low bitrates.

96–128 kbps stereo: More than enough for podcasts and interviews.
64–96 kbps mono: Ideal for lecture or meeting notes captured with a single microphone. It shrinks the file enormously while costing nothing in intelligibility.

On long spoken-word recordings this choice delivers the biggest win: encoding a three-hour meeting at 96 kbps mono rather than 320 kbps drastically reduces the file while leaving the content equally clear.

The difference between CBR and VBR

Constant bitrate allocates the same amount of data to every second of the recording. A completely silent passage receives the same budget as the densest moment of an orchestra. That means wasted data in quiet sections and a squeezed budget in dense ones. Its advantage is that file size can be calculated exactly in advance.

Variable bitrate distributes the budget according to need: tightening during simple passages and opening up during complex ones. The result is generally slightly better quality at the same average size. Today VBR is a widespread and sensible choice for archiving music.

The practical rule: VBR for a music library, CBR for technical scenarios that require a predictable data rate.

The most common misconception: gaining quality by raising bitrate

This is the single most frequent misunderstanding in audio conversion. If you have a 128 kbps MP3 and re-save it at 320 kbps, the lost information does not return. The frequency content discarded during MP3 encoding is not hidden somewhere inside the file — it was deleted. The new file merely holds the same incomplete audio in a wider container while wasting two and a half times the space.

Worse still, re-encoding adds a second round of loss. This time the encoder analyses audio that has already been compressed and makes fresh decisions on top of it. The result is usually a little worse than the original.

Bitrate choice therefore carries real meaning only on the first conversion from a lossless source. If you have a WAV, that conversion is your one chance — choose well. This is also the answer to why you should keep your original WAV files when converting WAV to MP3: if you change your mind, returning to the source is the only way to get a clean output at a different bitrate.

Three questions to ask before deciding

Where will I listen to this file? Studio headphones and a phone speaker do not demand the same precision.
Is the content music or speech? Speech tolerates far lower bitrates.
Am I keeping the source? If your WAV or FLAC archive is intact, you can afford to be bold and produce small files, because you can always go back and re-convert if needed.

In summary

Bitrate is the single setting that balances audio quality against file size, and the right value depends on the content. For music, 192–320 kbps covers most needs; for speech, 96–128 kbps does. Variable bitrate generally gives slightly better results at the same size. Most importantly: raising the bitrate does not restore quality lost in the past, which is why your real moment of decision is the first conversion from a lossless source.