Delivery & Formatting We can supply a large number of different format audio files. The most commonly requested types are Wave files (WAV) and MPEG Layer-3 (MP3). There are, however, many other audio file types that we can provide - detailed in the table below. It's worth noting the following: - The file type is usually determined by the file extension (what comes after the full stop in the filename). For example, ".wav" and ".mp3".
- The method used to compress and store the audio is call the codec (a contraction of COder and DECoder - describing the two basic functions of telecommunications equipment). This determines how small the file size is, and what it can be played back with.
- Some file types always use a particular codec. For example, MP3 files always use the "MPEG Layer-3" codec. Other files - like WAV files - support selectable codecs. For example, a WAV file can be encoded with the "PCM", "GSM6.10", "MPEG3" and 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 contain just the audio, whilst others contain additional header information (eg .MP3 files have information about artist, track, album, genre etc).
Audio File Formats | Open Formats | | WAV | Standard audio file format, used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD-quality sound files. Files of this type can be large in size - at around 10MB per minute of music. WAV files can be encoded with a variety of codecs to reduce the file size (for example the GSM or MP3 codecs). A list of common WAV file codecs can be found below. | | 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 mainly for music storage. | | OGG | A free, open source container format supporting a variety of codecs - the most popular of which is the Vorbis audio codec. Vorbis files are often compared to MP3 files in terms of quality, but the OGG format is not as widely supported. | | GSM | Designed for telphony use in Europe, the GSM format is very practical for telephone-quality voice. It offers a good compromise between file size and quality. WAV files can also be encoded with the GSM codec. | | FLAC | A lossless compression codec. If you compress a PCM file to FLAC and then restore it again it will be a perfect copy of the original. Most of the other codecs discussed here are lossy, which means a small part of the quality is lost during conversion. | | 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 basically 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 WAV 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. | | RAW | A RAW file can contain audio in any codec but is usually used with PCM audio data. | | | | | Proprietary Formats | | 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 with music downloaded from their iTunes service. | | ATRAC1 | The older style Sony ATRAC format. It always has a .wav extension. | | ATRAC2 | The newer style Sony proprietary format designed for Minidisc use. It has a .oma, .omg or .atp file extension. It's similar to MP3, and only used for reading or writing files from and to a Minidisc. | | RA | The 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 inside the file itself. | | DSS | Digital Speech Standard files are an Olympus proprietary format. Use GSM or MP3 if possible. | | MSV | Sony's proprietary format for Memory Stick compressed voice files. | | DVF | Sony's proprietary format for compressed voice files, commonly used by Sony dictation recorders. | | APE | Monkey's Audio gives about a 50% compression ratio, with no loss of quality. |
WAV File Codecs
| | | | Format | Bitrate | 1 min = | | 11,025Hz 16bit PCM | 176.4kbs | 1292k | | 8000Hz 16bit PCM | 128kbs | 937.5k | | 11,025Hz 8bit PCM | 88.2kbs | 646k | | 11,025Hz u-Law | 88.2kbs | 646k | | 8,000Hz 8bit PCM | 64kbs | 468.8k | | 8,000Hz u-Law (telephone quality) | 64kbs | 468.8k | | 11,025Hz 4bit ADPCM | 44.1kbs | 323k | | 8000Hz 4bit ADPCM | 32kbs | 234.4k | | 11,025Hz GSM6.10 | 18kbs | 131.8k | | 8000Hz Mp3 16k | 16kbs | 117k | | 8,000Hz GSM6.10 (mobile quality) | 13kbs | 102.5k | | 8000Hz Lernout & Hauspie SBC 12k | 12.0kbs | 87.9k | | 8,000Hz DSP Group TrueSpeech | 9kbs | 65.9k | | 8000Hz Mp3 8k | 8kbs | 60k | | 8,000Hz Lernout & Hauspie CELP | 4.8kbs | 35k |
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