Dateiformate für digitale Diktiersysteme

Introduction

There are a number of different types of Audio files. The most common are Wave files (wav) and MPEG Layer-3 files (mp3). There are, however, many other audio file types discussed below. The type is usually determined by the file extension (what comes after the . in the file name). For example, .wav, .mp3 or .dct.

The way the audio is compressed and stored is called the codec which determines how small the file size is. Some file types always use a particular codec. For example, .mp3 files always use the MPEG Layer-3 codec. Other files like .wav and .dct files support selectable codecs. For example, a .wav file can be encoded with the PCM, GSM6.10, MPEG3 and many other codecs. Be careful not to confuse the file type with the codec – it often surprises people to know you can have a MPEG Layer-3 encoded .wav file.

Some file types just contain the audio. But other file types can contain additional header information which can contain other information about the file (eg .dct files have information about the sender, priority, notes and other data in the file itself).

The information on this page is mainly directed towards users of our Customer Data Exchange System.

Offene Standards (herstellerunabhängig)

wav

Standard audio file format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD-quality sound files, which means that they can be large in size - around 10MB per minute of music. It is less well known that wave files can also be encoded with a variety of codecs to reduce the file size (for example the GSM or mp3 codecs).

mp3

The MPEG Layer-3 format is the most popular format for downloading and storing music. By eliminating portions of the audio file that are essentially inaudible, mp3 files are compressed to roughly one-tenth the size of an equivalent PCM file while maintaining good audio quality. We recommend the mp3 format for music storage. It is not that good for voice storage.

ogg

A free, open source container format supporting a variety of codecs, the most popular of which is the audio codec Vorbis. Vorbis files are often compared to MP3 files in terms of quality. But the simple fact mp3 are so much more broadly supported makes it difficult to recommend ogg files.

gsm

Designed for telphony use in Europe, gsm is a very practical format for telephone quality voice. It makes a good compromise between file size and quality. We recommend this format for voice. Note that wav files can also be encoded with the gsm codec.

dct

A variable codec format designed for dictation. It has dictation header information and can be encrypted (often required by medical confidentiality laws).

flac

A lossless compression codec. You can think of lossless compression as like zip but for audio. If you compress a PCM file to flac and then restore it again it will be a perfect copy of the original. (All the other codecs discussed here are lossy which means a small part of the quality is lost). The cost of this losslessness is that the compression ratio is not good. But we recommend flac for archiving PCM files where quality is important (eg. broadcast or music use).

au

The standard audio file format used by Sun, Unix and Java. The audio in au files can be PCM or compressed with the ulaw, alaw or G729 codecs.

aiff

The standard audio file format used by Apple. It is like a wav file for the Mac.

vox

The vox format most commonly uses the Dialogic ADPCM (Adaptive Differential Pulse Code Modulation) codec. Similar to other ADPCM formats, it compresses to 4-bits. Vox format files are similar to wave files except that the vox files contain no information about the file itself so the codec sample rate and number of channels must first be specified in order to play a vox file. Vox a very old file type and is pretty poor. We do not recommend it for anything except for supporting legacy systems.

raw

A raw file can contain audio in any codec but is usually used with PCM audio data. It is rarely used except for technical tests.

Proprietäre Standards (herstellerabhängig)

wma

The popular Windows Media Audio format owned by Microsoft. Designed with Digital Rights Management (DRM) abilities for copy protection.

aac

The Advanced Audio Coding format is based on the MPEG4 audio standard owned by Dolby. A copy-protected version of this format has been developed by Apple for use in music downloaded from their iTunes Music Store. Sample .aac file.

atrac (.wav)

The older style Sony ATRAC format. It always has a .wav file extension.

ra

A Real Audio format designed for streaming audio over the Internet. The .ra format allows files to be stored in a self-contained fashion on a computer, with all of the audio data contained inside the file itself.

ram

A text file that contains a link to the Internet address where the Real Audio file is stored. The .ram file contains no audio data itself.

dss

Digital Speech Standard files are an Olympus proprietary format. It is a fairly old and poor codec. Prefer gsm or mp3 where the recorder allows.

msv

A Sony proprietary format for Memory Stick compressed voice files. You might need a Sony plugin to load this.

dvf

A Sony proprietary format for compressed voice files; commonly used by Sony dictation recorders.