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audio file formats

Digital distribution of music online means there are numerous file types and formats to be aware of, we are going to take a look at both digital and analogue formats, the resultant files and some good practice when finalizing and exporting your music tracks.

A very prudent move is to always render a 24 bit stereo interleaved, un-dithered .wav file of your final mix down without any limiting on the master bus. The reason for this is that if at some stage your track receives a lot of attention and needs to be mastered professionally for release by a label or of course yourself you will have a very high quality version ready to go. This master will be very useful for a vinyl release as well as the lathe engineer will have greater sonic control when making a good sounding and decent level vinyl cut.

Wav or .aiff files

Wav or aiff files are great release formats simply because of their fidelity, uncompressed PCM (Pulse Code Modulation) audio that sounds exactly as you intended it to sound whether self finalized or professionally mastered. They can be 16 bit which is exactly the same specification as the files found on commercial Red Book CD releases. Correctly mastered and dithered 16 bit files are capable of reproducing a dynamic range which should keep most audiophiles happy in the vast majority of  listening conditions.

With a CD or 16 bit .wav / . aiff your fans and ultimately customers hear exactly what you wanted them to hear. Online it is remarkable that most online digital distribution service still only accept 16 bit files. 16 bit wavs are still, as of writing, the most common distributed audio file format. There are however exceptions. There are a few aggregators/distribution companies which will accept a 24 bit master but you should always check with them rather than assume. Of course if you are hosting the files on your own website you should be able to provide a 24 bit download version should you wish to. Strictly speaking there is no sonic advantage to a 24 bit master file in todays modern musical styles as there is typically very limited dynamic range. A 16 bit 96dB dynamic range capable file is perfectly able to present the dynamics of all music in any normal listening situation, some mastered music these days has less than 10dB of dynamic range.

Try for yourself:

You can bounce a 16 bit dithered or un-dithered file and a 24 bit file, align them identically on 2 stereo tracks and phase reverse one of the tracks. You will hear virtually silence, this is because they are virtually identical (assuming your DAW is working and coded correctly) with exception of the lowered “digital” noise floor of the 24 bit file. This noise floor (-74dB here in practical tests) will be inaudible in almost every normal listening situation, especially so with music with fairly limited dynamic range. Fidelity in the frequency domain is unaffected by the theoretical noise floor differences between 16 and 24 bit audio files.

Recent developments mean it is now possible to insert a ISRC code within a broadcast .wav file. This is ratified by the EBU (European Broadcasting Union) and now has it’s own very specific field. This is a very important development as it now allows the file to contain this all important unique identifying code.

Red Book CD

The red book CD release is a very common format still which contains 16 bit PCM master files. It has the potential for excellent sonic quality and is a convenient size for storage. It is popular amongst fans as it represents a complete package of music and artwork that a fan can enjoy in the physical world. EAN/UPC bar codes, ISRC codes and CD-Text (release title, track names and artist) can be embedded in a red book CD. The mastering engineer can deliver red book CD-R masters or use a special file format known as DDPi (disk description protocol) to a CD duplication plant.


Vinyl is seeing a resurgence, some people associate great sound with the vinyl format. This could be in part related to the audio processing used in mastering/cutting a lacquer for the format. (Or older recordings that were recorded to analogue tape before being mixed.) The sound reproduced from vinyl is not normally as heavily limited as those found on CD or digital files (though some high frequency limiting can be applied by a lathe engineer).

This may account for a slightly punchier sound with greater perceived dynamic range. Vinyl requires a fairly tight set of technical parameters to be applied before the music will transfer and reproduce well on the format. Special attention is required at the audio spectrum extremes (bass and extreme highs ) and care is required to avoid scratchy, distorted sibilance in the highs and upper mid range. Additionally there must be careful consideration for stereo bass sources.

This is required because of the physical manufacture process when cutting grooves on a lacquer and the subsequent replay of vinyl disks. A physical format with physical cutting and reproduction limitations.

For many vinyl has an association with “warm sound”, this can be the mastering approach as mentioned above and also that the top end rolls off (wears as diamond drags through the groove) quite quickly through wear with successive plays which tend to dull the sound and produce a warmer sonic footprint over time. Often peoples favourite albums are of vintage age and were recorded through world class analogue mixing consoles onto tape which gives a specific character of sound. Multiple reasons over and above the format itself contribute to the sound of vinyl. Vinyl can sound good or bad depending on the skill of the lathe engineer and the quality/maintenance level of his or her equipment.  

I normally provide 24 bit unlimited audio files as vinyl pre-master files, this means the lathe engineer can manipulate the files (even if just for a volume change) as he or she sees fit with least sonic degradation relative to a 16 bit file.

FLAC files (Free Loss less Audio Codec)

FLAC files are great, FLAC allows you to create, loss less files that compact the file size of your music by around 50pct. Few sites allow this but one that does is Bandcamp (also Soundcloud). FLAC is a great option because of the file size reduction. the downside being that the end user will often have to decompress the files using the FLAC application in order to hear them in some media players. Some progressive media players such as Video LAN (VLC Player) will allow the native streaming/playing of FLAC files. The FLAC Codec is freely downloadable.  

ALAC – Apple Loss less Audio Codec

Again another proprietary loss less format owned by Apple. Supported by iTunes.

MP3 files

The MP3 file is still viable but please do try not to encode at lower than 256kbps as fidelity will noticeably suffer. You have obviously worked very hard to create your music so present it in it’s best light. MP3 has a reasonable sound at 256kbps and above and smaller file sizes which is still convenient in these times where fibre optic broadband is not standard. Always ensure you keep a finished master/mix as a 16bit file for upload and distribution. (as well as a 24 bit unlimited version as mentioned in the beginning of this article)  MP3 has a specific tag available to encode an ISRC for royalty reporting..


AAC files are created when you release music on Apples iTunes typically at 256kbps, it is arguably better sounding than MP3 at the same rate though the differences are fairly small. It does seem to create low bit rate files such as 128 and 192kbps that sound slightly better than MP3. In general I do not recommend encoding any lossy files at lower than 256kbps if you want to produce a file that retains most of the details you have worked hard to create in your mix. It is possible to find freeware encoders such as iTunes and LAMEXP which can encode your files as AAC.

Mastered for iTunes (MFiT)

A development by Apple to marginally improve the fidelity of AAC data compressed files. In short digital tools provided by Apple allowing a mastering engineer to avoid ISP (Inter sample peak/ perceptual encoding filter) codec clipping of their AAC compressed fomat. Currently only high resolution files provided by “Apple content providers” can be marketed as “Mastered for iTunes”. “MFiT” requires at the very least a 24 bit / 44.1kHz audio file to be presented by an Apple content provider, high sample rates (where used in the actual recordings/DAW production) are recommended.

Ogg Vorbis

Odd name but yes a decent sounding free and open source compressed file format which is incidentally used by Spotify as it’s streaming codec. Some users of this format report that the codec sounds better than both MP3 and AAC files.

Compact Cassette

Don’t laugh, some bands from the DIY community (punky, shoe gaze, alternative genres) release their music on cassette albeit as a limited run, it is of course an antiquated and minority format. (many younger people have never owned a cassette deck in their entire life) However it is worth a mention as many grew up on cassette tapes. Generally speaking  a .wav that has been typically mastered for a digital release would translate well to the cassette format which has rather limited dynamic range and the risk of hiss creeping in during quiet passages of music. So fairly compressed and limited works well on cassette assuming the recording level is not too hot. Hovering around 0VU would be typical.   

Further detail about ISRC codes

ISRC codes are 12 digit unique identifying codes for each unique version of any track you make. They greatly help in tracking and recording of radio broadcasts of your music. An example would GBAAA1400001

Of the 12 characters naming the code the first 2 letters are country code, the next 3 registrant code, the next 2 year reference and then designation code for the track.

In the UK the designating body is PPL (Phonographic Performance Ltd.). Find out who issue ISRC codes in your country, become a registrant and you will be able to obtain ISRC codes for your music track releases. ISRC codes are possible to insert or embed into various file formats and this is typically undertaken during the mastering stage. The ISRC code is often used to track radio broadcast transmissions and ensure that the artist, publisher or record label is paid a royalty for the use of the recording. At this time ISRC codes can be embedded in broadcast .wav files, Red Book CD releases and MP3 files.

Feel 100pct free to share this on audio forums and social media etc. The more, the merrier ! 

Copyright Barry Gardner 2014