# Tempo Matcher Detect a loop BPM and time-stretch it to your project tempo — manual BPM or a reference track, with the output BPM re-verified after stretching. > Canonical page: https://elysiatools.com/en/tools/tempo-matcher - **Category:** Media - **Keywords:** tempo matcher, time stretch, bpm match, loop to bpm, atempo, rubberband, bpm detection, loop stretching, loop pack, 变速 ## Overview The loop tempo comes from onset-envelope autocorrelation over the full track. The target is either a BPM you type or a reference track that gets the same analysis (great for building loop packs around an acapella or a live drummer). The stretch ratio drives a pitch-preserving engine: rubberband when the FFmpeg build has it (best quality), otherwise the atempo filter chained within its 0.5-100 per-instance range — atempo is the faster WSOLA-style stretcher and is the engine on most builds. A whole-bar trim option cuts the stretched result to complete 4/4 bars at the target tempo so the loop cycles cleanly. The output is re-analyzed after stretching and its measured BPM is reported next to the target, so the match is verified end to end. Extreme ratios (beyond roughly 0.5x-2x) sound smeared on any engine — prefer repitching or cutting a different loop. ## Inputs - **Loop or sample** (file) - **Speed source** (select) - **Target BPM** (number): e.g. 128 - **Reference track** (file) - **Engine** (select) - **Trim to whole bars (4/4)** (checkbox) - **Output Format** (select) ## When to use - Aligning drum loops and rhythm samples to a specific project BPM without shifting pitch. - Synchronizing instrumental stems directly to the tempo of an imported reference track. - Trimming stretched loops to exact 4/4 bar lengths so they cycle seamlessly in your DAW. ## How it works - Upload your primary audio loop or sample. - Choose whether to set a target BPM manually or analyze a reference track to determine the speed. - Select your processing engine (Rubberband or atempo) and choose whether to trim the result to complete 4/4 bars. - Pick your preferred audio format (WAV, MP3, FLAC, M4A, or OGG) and download the tempo-verified file. ## Use cases - Preparing uniform tempo-matched sample packs for music distribution. - Matching percussion grooves to unquantized live instrumentation or acapellas. - Adapting existing project stems to fit updated tempo arrangements. ## Frequently asked questions ### Does time-stretching change the pitch of the audio? No, both available engines adjust playback speed while maintaining the original musical pitch. ### What is the difference between Rubberband and atempo engines? Rubberband delivers higher acoustic quality with fewer artifacts, while atempo provides faster WSOLA-based processing. ### How does matching by reference track work? The tool uses onset-envelope autocorrelation on the reference track to detect its BPM and applies that target to your source loop. ### What does the whole-bar trim option do? It cuts the stretched audio cleanly at full 4/4 bar boundaries so the sample loops without timing gaps. ### What file formats are supported for output? You can export the tempo-matched audio in WAV, MP3, FLAC, M4A, or OGG formats. ## Related tools - [Audio Add Silence](https://elysiatools.com/en/tools/audio-add-silence): Add a specified duration of silence to the start or end of an audio file - [Air Band Enhancer](https://elysiatools.com/en/tools/audio-air-band-enhancer): Brighten dull vocals or masters with a high air shelf plus an exciter that synthesizes new top-end harmonics — the Aphex Aural Exciter architecture built from FFmpeg. - [Album Loudness Matcher](https://elysiatools.com/en/tools/audio-album-loudness-matcher): Match a batch of tracks to one target loudness the way album gain works: one gain for the whole record keeps intentional inter-track dynamics, hybrid mode only tames outliers, per-track mode flattens everything. - [Audio Ambience Loop Generator](https://elysiatools.com/en/tools/audio-ambience-loop-generator): Extract the background ambience/room tone from a fragment and generate a seamless loop of any target length. - [Audio Automatic Fade Designer](https://elysiatools.com/en/tools/audio-automatic-fade-designer): Design and render musical fade-ins and fade-outs: bar-based lengths at your BPM or lengths auto-derived from detected silence, fades placed against the real music span, logarithmic curves, optional silence trimming. - [Batch Audio Normalize](https://elysiatools.com/en/tools/audio-batch-normalize): Normalize multiple audio files to a target peak level with consistent volume across the batch - [Audio Beat Matcher](https://elysiatools.com/en/tools/audio-beat-matcher): Adjust tempo to match a target BPM - [Audio Breath Control Editor](https://elysiatools.com/en/tools/audio-breath-control-editor): Detect breaths in speech and naturally crossfade to reduce, remove, or keep them. ## Samples - [Copyright-Free FLAC Audio Samples](https://elysiatools.com/en/samples/flac-samples): Lossless FLAC audio samples for testing and development, mirrored from MP3 set with nature sounds and meditation music - [Copyright-Free MP3 Audio Samples](https://elysiatools.com/en/samples/mp3-samples): Collection of royalty-free audio samples for testing and development purposes including nature sounds, meditation music, and ambient audio - [Copyright-Free WAV Audio Samples](https://elysiatools.com/en/samples/wav-samples): Uncompressed PCM WAV audio samples for testing and development, mirrored from MP3 set with nature sounds and meditation music - [Copyright-Free Raw PCM Audio Samples](https://elysiatools.com/en/samples/pcm-samples): Raw PCM s16le audio samples featuring nature ambience and relaxing music for waveform, playback, and conversion workflows