3Run it; the time-stretch preserves pitch, so voices stay natural instead of transposing upward.
4Download the retimed FLAC file — shorter or longer in exact proportion, with the bitrate and sample rate untouched.
Change FLAC Speed FAQ
How does Change FLAC Speed change the playback rate?
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Concretely, the time-stretch is applied to the PCM directly and written back losslessly, which is why a lossless source is the right input for anything above about 1.5x where artefacts start to show. Choose a multiplier — 0.5x for half speed, 2x for double — and the whole file is retimed.
Will speeding it up make voices sound high-pitched?
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No. The time-stretch preserves pitch, so a 1.5x speech track sounds like the same person talking faster rather than like a chipmunk. That is the difference between a proper time-stretch and simply playing the samples faster.
Does the source format affect the result?
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It does. FLAC is lossless compression — bit-identical to the source on decode, at about half the size of WAV. That determines whether the retimed result can be written back cheaply or has to be fully re-encoded.
Anything specific to FLAC here?
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Yes — FLAC decodes bit-identically to the source, so any number of edit-and-resave cycles cost you nothing in fidelity. Worth knowing before you commit to a large speed change.
How far can I push the speed before it sounds wrong?
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Roughly 0.75x to 2x is transparent for speech. Beyond about 2.5x the stretch artefacts become audible on any algorithm, and below 0.5x the reconstruction has to invent too much. Music tolerates far less than speech does.
Does the file get shorter, and does it get smaller?
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Shorter, yes, and in exact proportion — an hour of audio at 1.5x is forty minutes. The file shrinks by roughly the same proportion because there is less material to encode. The bitrate, the sample rate and the channel layout are all left exactly as they were.
What can I upload to Change FLAC Speed?
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WAV, FLAC and AIFF, at any bit depth and sample rate up to and including 24-bit/192 kHz. Lossy files work in the same batch if you are mixing sources.
Is there a file size limit on Change FLAC Speed?
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Yes: free accounts process audio up to 15 MB per file — for uncompressed PCM that is roughly twenty minutes of CD-quality stereo, so it is a real limit here in a way it is not for MP3. If you are over it, converting WAV to FLAC first is the free fix — it is lossless and roughly halves the size.
Will Change FLAC Speed lower the quality of my FLAC audio files?
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No. Lossless audio is edited sample-exactly, so what comes back decodes bit-identically to what you would get doing the same edit in a desktop editor. You can repeat the cycle as many times as you like without accumulating any loss at all.
Can I run Change FLAC Speed on several FLAC audio files at once?
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Yes, though lossless files are large, so the batch is bound by upload bandwidth rather than by processing. Settings apply uniformly across the set.
Are bit depth and sample rate preserved?
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Yes, unless you change them deliberately. A 24-bit/96 kHz source stays 24-bit/96 kHz — nothing is silently downsampled to 16/44.1, which is the failure mode that makes a master unusable.
Does Change FLAC Speed cost anything?
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No. Change FLAC Speed is free without an account, and nothing is added to the audio. The upload and the result are deleted automatically about 24 hours after the job, which leaves time to download the result.
