FSSD to AU Converter

Online FSSD to AU converter — quick and straightforward

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Modern Format

Moving from FSSD to AU transitions your audio from an obscure encoding to standard Unix audio format — a significant practical improvement.

Browser-Based

The converter is entirely web-based. Convert FSSD to AU without downloading or installing any application on your device.

Batch Processing

Got a collection of FSSD recordings? Upload them in one batch and convert the entire set to AU in a single session.

How to convert FSSD to AU

1

Select files from Computer, Google Drive, Dropbox, URL or by dragging it on the page.

2

Choose au or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your au file right afterwards

About formats

FSSD is a raw audio format that originated in the classic Macintosh ecosystem, where Farallon Computing's MacRecorder hardware (1988) stored digitized sound as unsigned 8-bit PCM in resource fork entries tagged with the 'FSSD' type code. In modern audio processing tools such as SoX, FSSD is treated as an alias for the u8 (unsigned 8-bit) raw format — headerless files containing a flat stream of single-byte amplitude samples, where each value from 0 to 255 represents an audio level with 128 as the center point. Because there is no header, playback parameters like sample rate and channel count must be provided externally. The original MacRecorder typically captured at rates up to 22 kHz in mono, though any sample rate is valid when interpreting the raw data. FSSD and its compressed companion format HCOM (which adds Huffman compression to the same underlying data) were the standard audio formats for early Mac multimedia: HyperCard stacks, educational CD-ROMs, and system alert sounds of the late 1980s and early 1990s relied heavily on this encoding. One advantage of the raw FSSD format is trivial parseability — with no container overhead, the audio data begins at byte zero and can be read by any tool capable of processing unsigned 8-bit PCM. The format's historical significance also makes it practically relevant for digital archivists: converting FSSD recordings to modern containers like WAV preserves the original audio content losslessly, since the raw samples only need a header prepended, not any form of transcoding.
Developer: Farallon Computing
Initial release: 1988
AU is an audio file format introduced by Sun Microsystems for its Unix workstations and the NeXT platform. It features a minimal 24-byte header specifying data offset, size, encoding type, sample rate, and channel count, followed by the audio payload. AU supports numerous encodings, including uncompressed linear PCM at various bit depths, mu-law and A-law companding (logarithmic compression used in telephone systems), and several ADPCM variants. This versatility made AU a workhorse across early Unix environments, web audio (Java applets defaulted to AU), and telephony applications. One advantage is simplicity: the compact header and straightforward structure make it trivial to parse, generate, and stream programmatically. The built-in mu-law option provides another benefit, delivering reasonable voice quality at just 8 KB per second — half the rate of 16-bit uncompressed audio — invaluable when storage and bandwidth were scarce. Although modern formats have largely supplanted AU in consumer applications, it retains a foothold in scientific computing and audio processing pipelines where minimal overhead and reliable cross-platform behavior are valued.
Developer: Sun Microsystems
Initial release: 1992

Frequently Asked Questions

Why convert FSSD to AU?

Since FSSD has minimal raw PCM format not suitable for modern workflows, switching to AU provides simple well-documented structure.

How do I open a AU audio?

You can open AU with VLC, Audacity, SoX, and Unix/Linux media players.

Will I lose audio quality converting FSSD to AU?

Converting to AU is lossless — the audio quality in the AU output will be identical to the original FSSD recording.

Can I convert FSSD to AU on any device?

Yes — the converter runs entirely in your browser, so it works on Windows, macOS, Linux, and mobile devices alike.

Can I convert multiple FSSD recordings at once?

Yes — upload several FSSD recordings simultaneously and they will all be converted to AU in parallel, saving you time.

Does FSSD to AU conversion cost anything?

Standard conversions are available at no cost. Paid plans unlock higher limits and faster processing for heavy usage.