Audio Speed Changer
Many pages that answer "audio speed changer" want an upload and an account before anything plays. This one decodes the file in this browser tab, draws the waveform before and after, and plays it on a press, and it is explicit about the thing every other page blurs: there are two different ways to change speed and they do not sound alike. Speed holds the pitch, using the time stretch already built into your browser, so a lecture at 1.5x still sounds like the person talking. Speed + pitch couples them the way a tape machine does, so 2x is exactly half the length and exactly one octave up, and the page prints the semitone number. Reverse and Gain work on the same file, with no upload either. The export follows the same arithmetic the preview does, with one exception the page never hides: the browser will not render its time stretch to a file, so pitch-preserved speed plays and does not export, while rate-coupled speed, reverse and gain all write a 16-bit PCM WAV. The ceilings are 120 MB and 30 minutes, checked before the file is read and before anything is allocated, because the whole file is held as 32-bit samples in this tab rather than on somebody's server.
Open an audio file
· or drop one anywhere on the stage
Ready. Choose an audio file, or drop one on the stage.
Speed takes any value between 0.25x and 4x: type it in the field as 1.25x or 125%, press the up and down arrows to move it 0.05 at a time, or press one of the chips on the stage. In Speed + pitch the semitone field sets the speed to match, so +12 semitones is 2x. Space plays and stops. The ceilings are 120 MB and 30 minutes, because the whole file is decoded to 32-bit samples in the memory of this tab. Gain runs from -24 dB to +24 dB and plays back at 50% of the level it writes, so a boost does not arrive at full volume in your headphones, and the readout counts the samples that clip before you download anything. The file is never uploaded and never sent anywhere.
Common questions
- Does speeding audio up change the pitch?
- It depends which of the two modes you are in, and that is the whole reason this page has both. Speed asks the browser to hold the pitch while it stretches the time, which is what you want for a lecture, a podcast or an audiobook: 1.5x is shorter, the voice is still the voice. Speed + pitch does what a tape machine or a record player does, coupling the two, so 2x is one octave up and 0.5x is one octave down. The page shows the shift in semitones, worked out as 12 times the base-two logarithm of the rate, so 1.25x reads +3.86 semitones. If your browser does not provide a time stretch, the Pitch cell says so rather than pretending: in that browser the pitch moves with the rate, and the page tells you before you press Play.
- Can I download the file at the new speed?
- Rate-coupled speed, reverse and gain all download as an uncompressed 16-bit PCM WAV. Pitch-preserved speed does not: the Export cell reads Plays only and the page says why, instead of failing quietly. The reason is specific: holding the pitch while the time changes means resynthesising the audio, the browser has exactly one such engine and exposes it for playback only, with no way to render it into a buffer a page can write out. Everything else is sample arithmetic this page can do itself. The rate-coupled export is the cleanest of the three, because it changes no sample at all: the same samples are written with the sample rate in the WAV header multiplied by the speed, which is precisely what playing a recording faster means. A header holds a whole number of hertz, so 1.234x on a 44.1 kHz file is written at 54,419 Hz rather than 54,419.4 Hz, and the page prints the header rate it writes.
- Which files can I open, and is there a size limit?
- Whatever your browser can already decode, which is the honest answer because the decoding is the browser's own: in practice MP3, WAV, M4A and AAC, OGG and Opus, and FLAC in current versions of Chrome, Firefox, Safari and Edge. There is no separate list maintained here and nothing to keep up to date. The two ceilings are 120 MB of file and 30 minutes of decoded audio. Neither is a commercial gate, since nothing is uploaded and there is nothing to charge for. They exist because decoding expands audio: 30 minutes of stereo at 48 kHz is about 691 MB of 32-bit samples held in this tab before a byte of WAV is written, and reversing or gaining it allocates about that much again. The size is checked against the file before it is read and the length against the decoded audio before anything is allocated, so a file past either ceiling gets a message naming the limit and its own value instead of a frozen tab.
- Is reversing audio here lossless?
- The reverse itself is exact. Every sample is written in the opposite order and nothing else is touched, so the length, the pitch and the sample rate all come out the same as they went in, and reversing the result gives back the original sample for sample. That property is asserted in this tool's tests rather than assumed. Two honest details sit alongside it. The file you open is decoded first, so anything a lossy encoder already discarded is gone before this page sees it, and the WAV is written at 16 bits, which rounds the browser's 32-bit float samples to the nearest 16-bit value. Neither is a second compression pass, and the download is never re-encoded.
- How much can I raise the volume of a quiet recording?
- The gain control runs from -24 dB to +24 dB, and it is plain multiplication: amplitude equals 10 to the power of the decibels over 20, so +6 dB is roughly double the amplitude and -6 dB is roughly half. The page prints that formula next to the result. Raising a quiet track has a hard limit, which the readout makes visible: the loudest sample decides how much headroom there is, and past that point samples hit full scale. They are clamped there rather than allowed to wrap, because a wrapped sample flips sign and cracks exactly where the audio was loudest, and the readout counts how many samples would clip before you download anything. The preview plays at half the level it writes, so a boost does not arrive at full volume through headphones, while the exported WAV carries the whole gain.
- Is my audio uploaded anywhere?
- No. The file is decoded by this browser, the waveforms are drawn on a canvas here, and the WAV is written by JavaScript in this tab and handed to the browser's own download. There is no upload, no queue, no account and no request of any kind, so no part of the audio reaches a server, an analytics call or an error report. The only thing kept between visits is the setting row: which mode you were in, the speed and the gain, stored in this browser under a single key. The Start over button at the top of the page forgets it, and a browser with storage blocked simply opens at the defaults.
- Can I use it without a mouse?
- Yes. The speed is an ordinary text field: type 1.25x, or 125%, or just 1.25, and press Enter. With that field focused the up and down arrows move the speed by 0.05 at a time, and in Speed + pitch the semitone field takes +12 or -5 and sets the speed to match. The gain field works the same way, moving a decibel per arrow press. The space bar plays and stops from anywhere outside a field or a button, the mode buttons and the speed chips are ordinary buttons in the tab order, and anything typed that is not a number is refused with the form to type instead, rather than quietly becoming 1x.
Playback speed is exact and the new length is the old one divided by the rate. Pitch preservation uses the browser's own time stretch, is not available in every browser, and cannot be written to a file: only a rate-coupled speed change, a reverse or a gain change exports as WAV. Gain multiplies every sample and clips at full scale, and the page counts the clipped samples before you export.