Free Audio Compressor & Converter

What Do Codec, Bitrate, and Channel Settings Mean?

Codec Choice

AAC (Advanced Audio Coding) is the successor to MP3 and produces noticeably better quality at the same bitrate. It is the native codec for iOS, macOS, YouTube, and most streaming platforms. MP3 offers near-universal hardware and software support, including car stereos and old devices. Opus is the most efficient codec at bitrates below 128 kbps, making it ideal for voice and podcast delivery.

Bitrate

Bitrate is the primary lever for file size. Unlike video's CRF, audio bitrate is set directly in kbps. 64–96 kbps is transparent for voice and podcasts. 128–192 kbps covers most music listening scenarios. 256–320 kbps is reserved for audiophile use or archival masters where maximum fidelity is required. File size scales linearly: 256 kbps produces exactly twice the bytes of 128 kbps for the same duration.

Sample Rate & Channels

Sample rate (Hz) determines the highest frequency the audio can reproduce. 48 kHz is the broadcast standard; 44.1 kHz is the CD standard. Dropping to 22 kHz saves space but removes high-frequency content above ~11 kHz, which is noticeable for music. Converting stereo to mono halves the data for single-speaker content like podcasts and audiobooks, with no audible downside.

Compress an Audio File in Four Steps

How Does Bitrate Control Audio File Size?

Audio encoders work differently from image encoders. Instead of a quality percentage, they target a specific data rate in kilobits per second. The file size is therefore predictable: a 30-minute podcast encoded at 96 kbps mono AAC will always produce a file of approximately 21 MB, regardless of how quiet or loud the content is. This makes bitrate a precise budgeting tool — if you need a file under a specific size, you can calculate the required bitrate before encoding.

The perceptual quality threshold differs significantly between codecs. AAC achieves near-transparent quality for music at 128 kbps. MP3 requires around 160–192 kbps to reach the same perceived quality. Opus surpasses both at low bitrates — 64 kbps Opus is widely considered cleaner than 128 kbps MP3 for voice content. If your goal is the smallest possible file that still sounds acceptable for speech, Opus at 48–64 kbps mono is the optimal choice. For music that will be played on good speakers or headphones, AAC at 192 kbps is a reliable floor.

Audio Compression FAQ — Common Questions Answered

Is my audio uploaded to any server?

No, your audio files are never uploaded. All compression happens locally in your browser using WebAssembly (FFmpeg.wasm). Your files remain completely private and secure on your device. You can even disconnect from the internet after the page loads and continue compressing audio.

Which codec should I choose?

AAC offers the best quality-to-size ratio and works on all modern devices. MP3 has universal compatibility with older devices. Opus provides superior compression, especially at lower bitrates, but has limited support on older devices.

What bitrate should I use?

128-192kbps is ideal for most music. 64-96kbps works well for podcasts and voice recordings. 256-320kbps is for audiophiles or when maximum quality is needed. Higher bitrates mean better quality but larger file sizes.

How much smaller will my audio file be?

File size reduction depends on the source format and your settings. Converting WAV or FLAC to AAC at 128kbps typically reduces file size by 80-90%. MP3 to AAC at the same bitrate usually achieves 10-30% reduction.

Should I convert stereo to mono?

For voice recordings, podcasts, and audiobooks, mono is usually sufficient and reduces file size by approximately 50%. For music, keep stereo to preserve the spatial audio experience unless file size is critical.

What audio formats are supported?

We support almost all audio formats including MP3, M4A, AAC, WAV, FLAC, OGG, Opus, AIFF, WMA, and many more. Powered by FFmpeg, LocalSquash can handle virtually any audio format. Output formats are AAC (M4A), MP3, or Opus, depending on your codec selection.

Will compressing reduce audio quality?

Yes, lossy compression (AAC, MP3, Opus) reduces quality slightly, but at 128kbps or higher, most people can't hear the difference. The human ear is less sensitive to audio quality loss compared to video quality loss, making compression very effective for audio.

How do I convert WAV to MP3?

Simply upload your WAV file and select MP3 as the output codec. Choose your preferred bitrate (128-320kbps) and click compress. The conversion typically reduces file size by 80-90% while maintaining good quality.

Can I trim audio files?

Yes! LocalSquash includes audio trimming. Set the start and end times to extract only the portion you need. This is perfect for creating ringtones, sound clips, or removing silence from recordings.

What's the best format for podcasts?

For podcasts, we recommend AAC or MP3 at 96-128kbps mono. This provides excellent speech clarity while keeping file sizes small. AAC typically produces slightly better quality at the same bitrate.

How do I compress an MP3 file?

Upload your MP3 file to LocalSquash, select MP3 as the output codec, and choose a lower bitrate than the original (e.g., 128kbps instead of 320kbps). Click compress and the smaller MP3 will download automatically. You can also convert stereo to mono to cut file size in half, which is ideal for voice recordings and podcasts.

How do I compress a WAV file?

WAV files are uncompressed audio and are typically very large. Upload your WAV file and select AAC or MP3 as the output codec at 128-192kbps. This usually reduces file size by 80-90% while maintaining excellent quality. For example, a 50 MB WAV file typically compresses to 5-10 MB as MP3 at 128kbps.

How do I convert AAC to MP3?

Upload your AAC or M4A file to LocalSquash and select MP3 as the output codec. Choose your preferred bitrate (128-320kbps) and click compress. The conversion happens entirely in your browser using FFmpeg. MP3 is the best choice when you need maximum compatibility with older devices, car stereos, and embedded audio players.

How do I convert FLAC to MP3?

Upload your FLAC file and select MP3 as the output codec. FLAC is a lossless format, so you have full flexibility to target any MP3 bitrate without generation loss concerns. At 192kbps MP3, a typical 30 MB FLAC album track compresses to about 4-5 MB with quality that's indistinguishable to most listeners.

How do I convert OGG to MP3?

Upload your OGG/Vorbis file to LocalSquash and select MP3 as the output codec. Since OGG is already a lossy format, use at least the same or higher bitrate as the source to minimise additional quality loss. MP3 output ensures your audio plays on every device including older hardware that doesn't support OGG.

What is the difference between AAC and MP3 at the same bitrate?

At 128 kbps, AAC generally produces noticeably cleaner audio than MP3 — particularly in the high frequencies (cymbals, sibilance, breath sounds) where MP3's older algorithm introduces more distortion. At 256 kbps and above, both codecs are transparent for most listeners. The main reason to still use MP3 is device compatibility — car stereos, older Bluetooth speakers, and some embedded systems only support MP3.

Why is Opus better than MP3 at low bitrates?

Opus uses a hybrid CELT/SILK architecture that was designed specifically for real-time and streaming use cases where bandwidth is limited. At 48 kbps, Opus models voice and music using a combination of speech-optimised (SILK) and general-audio (CELT) coding, while MP3 at the same bitrate lacks the algorithmic headroom to handle anything but the most basic waveforms cleanly. The downside is that Opus files (.opus) are not yet playable in all environments.

How much does converting stereo to mono save?

Exactly 50% of the audio data, since mono encodes one channel instead of two. For a 30-minute stereo podcast at 128 kbps (approx. 28 MB), converting to mono at 64 kbps produces a file of roughly 14 MB. For voice content recorded with a single microphone, most listeners cannot hear any difference between the stereo and mono versions.

Can I compress a lossless FLAC or WAV file without quality loss?

Not with lossy codecs (AAC, MP3, Opus) — by definition they discard audio information. If you need to reduce a FLAC or WAV file while keeping it lossless, the only option is to re-export as FLAC with a lower sample rate (e.g., 44.1 kHz instead of 96 kHz) or reduce bit depth. For archival, keep the lossless original and create a separate AAC or Opus version for distribution.

What sample rate should I use?

For music, 44.1 kHz (CD standard) is the universal safe choice. For podcast and voice content, 44.1 kHz or 48 kHz are both fine — 48 kHz is the broadcast standard used by radio and video. Dropping to 22 kHz removes frequencies above ~11 kHz, which is audible on music but mostly inaudible for speech.

What output formats does LocalSquash produce?

Output is AAC encoded inside an M4A container, MP3, or Opus inside an OGG container. M4A/AAC plays natively on iOS, macOS, Android, Windows 10+, and all major browsers. MP3 plays on virtually every device ever made. Opus/OGG is supported by all modern browsers and Android, but may require a separate app on older iOS versions.

How to Get the Smallest Audio File Size

Convert Audio to MP3 — WAV, FLAC, AAC & OGG

MP3 is the most universally compatible audio format — it plays on every device, car stereo, Bluetooth speaker, and media player ever made. LocalSquash converts any audio format to MP3 using the same FFmpeg LAME encoder used by professional audio tools. Simply upload your file, select MP3 as the output codec, choose your bitrate, and click compress.