無料オンライン音声再生速度変更ツール

音声再生速度を変更する4つの手順

Changing the playback speed of an audio recording is essential for podcasters, students, language learners, musicians, and audio editors. Whether you want to speed up a 60-minute university lecture to 1.5x speed to save 20 minutes of study time, slow down a rapid foreign language dialogue to 0.75x to catch every syllable, or adjust the tempo of a voiceover track to fit a video timeline, our online audio speed changer provides a fast, reliable, studio-grade solution.

Unlike basic tools that rely on remote cloud servers, our tool runs 100% inside your web browser. It utilizes high-performance digital signal processing algorithms to perform sample-accurate time stretching right in your device's memory. You get instant speed adjustments, real-time audio auditioning, and immediate downloads without any wait time.

操作手順ガイド：

1. Upload Your Audio File: Drag and drop your audio recording into the intake zone above, or click to choose an MP3, WAV, M4A, AAC, FLAC, or OGG file from your computer or phone. Files up to 150 MB are supported.
2. Select Your Desired Speed: Click one of our instant speed presets (such as 0.75x, 1.25x, 1.5x, or 2.0x), or drag the fine-tuning slider to select any custom multiplier between 0.25x and 4.0x with 0.05x precision.
3. Choose Pitch Mode: Keep the default Preserve Pitch (Natural Voice) mode to ensure speakers retain their natural vocal tone without sounding like chipmunks or deep demons. Or switch to Shift Pitch if you want the classic analog tape/vinyl speed effect.
4. Audition & Process: Click Audition at Selected Speed to listen to the new tempo in real time. Once satisfied, click Process Audio Speed Now to generate pre-encoded 192k MP3 and Lossless WAV files ready for instant download.

タイムストレッチとリサンプリングの違い：声が高くならない仕組み

When you speed up a traditional physical recording (such as a vinyl record or analog cassette tape), the playback mechanism spins faster. As a consequence, audio frequencies are compressed in time, causing the perceived pitch to rise proportionally. Doubling playback speed (2.0x) shifts the pitch up by an entire octave (+12 semitones), creating the infamous high-pitched "chipmunk effect."

In modern digital speech processing, listeners want to speed up audio files—especially spoken-word podcasts, audiobooks, and conference lectures—while keeping human voices completely natural. This acoustic feat is called Time-Scale Modification (TSM) or pitch-preserving time stretching.

Our audio speed changer gives you total control over both methods:

• Preserve Pitch (WSOLA Engine): Uses Waveform Similarity Overlap-Add to stretch or compress time while preserving the original frequency spectrum. A human voice speaking at 1.5x sounds energetic and fast, but retains its exact vocal timbre and pitch.
• Shift Pitch (Resampling Engine): Linearly interpolates samples so that pitch and tempo rise and fall together. This is ideal for sound design, DJ effects, video comedy, and vintage tape emulation.

WSOLAアルゴリズムによる位相制御の原理

How does pitch-preserving time stretching work under the hood? Our engine utilizes the WSOLA (Waveform Similarity Overlap-Add) algorithm, one of the most respected DSP techniques for spoken voice and acoustic audio.

The algorithm divides the incoming audio stream into overlapping analysis frames (typically 20 to 30 milliseconds in length). When speeding up audio, the spacing between consecutive frames is widened. However, if frames are simply stitched together arbitrarily, the peaks and troughs of the sound wave can collide out of phase, creating a hollow, comb-filtered sound that ruins speech intelligibility.

WSOLA solves this through cross-correlation phase alignment. For every frame, the algorithm searches a small tolerance window to locate the exact sample position where the waveform wave cycles match the preceding audio. It then applies a raised-cosine Hann window to overlap and add the frames seamlessly. For stereo recordings, our engine calculates alignment across both channels synchronously, ensuring that stereo imaging and phase stability are strictly maintained.

Popular Audio 再生速度倍率s & Use Cases

Choosing Your Export Format: 192k MP3 vs. Lossless Studio WAV

Once your audio speed is processed, you are provided with two immediate download options, pre-rendered simultaneously in browser memory:

• MP3をダウンロード (192 kbps CBR): The industry-standard format for web publishing, podcasts, smartphones, and car stereos. It reduces file size by ~90% compared to raw WAV while delivering crisp, broadcast-quality voice clarity.
• WAVをダウンロード (16-bit PCM 48 kHz): The uncompressed studio master format. It preserves every bit of digital acoustic detail, making it the ideal choice for importing into digital audio workstations (DAWs) like Adobe Premiere, Audition, DaVinci Resolve, or Pro Tools.

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