Download music formats
different types, compression and uploads

Why use different formats?

In 1995 the only compressed audio format for public use on the web was MP3, and sharing full bandwidth music files over dial-up connections was completely out of the question. Today there is a bewildering array of formats. Broadband is available to 20 million households and about 40 million people in the UK, and about 2 billion people globally (2010). MP3 or AAC are still the most common download formats so things haven’t changed a lot in practice.

Broadband will make bigger files and lossless encoding increasingly feasible, and new high-compression formats like Ogg Vorbis and MP4 (Advanced Audio Coding, AAC) have a number of advantages, but they’re not for universal use just yet.

More open download formats

There are many file formats. These are the main, more open formats. This means they are independent of particular manufacturers, easy to move between operating systems and more widely accessible.

Ogg FLAC and Vorbis are proper open standards. FLAC is a lossless codec and compresses a CD to about half the original size. Vorbis is a lossy codec and compresses to around 10% like MP3 but sounds better. There is no danger of Ogg being limited by its owners and it is increasingly popular but still less common than MP3.

Full bandwidth music files from unprotected CDs play on most jukebox software and are now feasible but still lengthy downloads on fast broadband. They are easily stored in WAV or AIFF (PCM) formats which are easily translated between platforms without loss of quality.

MP3 is still the best way to put music on your web site. Proprietary formats like Flash, Real Audio, Quicktime (QT) and even Windows Media Audio (WMA) have a smaller audience. Most PCs, Macs and other systems (e.g. Linux) can play MP3s and they’re as small you can get with today’s compression—about 10% of the equivalent CD file size. The downside of MP3 is sound quality but if you want to be heard by the largest audience it’s the only choice for broadcasting from your site. I wouldn’t sell MP3 because AAC, WMA and Ogg are just as easy to make and sound much better.

MP3 isn’t an open standard and the owners could charge for it in some way. But I group it with “more open” formats for now.

Less open download formats

These are the main proprietary file formats. This means they are dependent on certain manufacturers, less easy to move and lack universal access.

With shellac, vinyl, CD and cassette, people became used to universal, play-anywhere media they could copy. Mainstream Internet music is still very primitive and there are many barriers to useability.

Proprietary formats include Real, Apple AAC, Sony ATRAC, and Windows Media with various DRM options. Some of these are licensed (Windows, Sony) others aren’t (Apple). All have a limited audience and most are only available through particular players. Download aggregators help to reduce this complexity for content providers, and it is possible to offer these formats without encoding them all yourself.

Multimedia formats include Apple Quicktime, MS Windows Media, Macromedia Flash or Shockwave. These formats use more expensive authoring software and have a smaller audience.

Real Audio is a RealNetworks proprietary file format compressed using a system called CELP. Basic Real encoders and players are available free. Media files are compressed by matching slices of data against a library of waveforms and replacing them with codes. These codes are turned back into media data by looking up the same library in the player. CELP is also used in mobile phones. Real player advertising and registration are quite intrusive for users and a significant section of the online community simply won’t install it.

RealNetworks products and web sites use and play a number of other codecs beside Real Audio, including WMA and AAC (not the Apple flavour).

MiniDisc (discontinued in mid-2007) was a consumer format controlled by Sony which used compression called ATRAC. It had built-in copy-protection (SDMI) and interface limitations to prevent sharing ATRAC files. The OpenMG jukebox and EMB Internet connection used by NetMD were also designed to lock-down content, even on domestic recordings.

WeedShare, PassAlong and other files of this type wrapped audio in cascading DRM that paid content owners and users for onward sharing and sales. These were proprietary when they used WMA and required Windows (they were not cross-platform). As far as I know this kind of file-sharing format is now extinct.

Masters and compressed copies

It is best to regard PCM/CD (WAV, AIFF) files as masters and any compressed copies as one-offs for a specific purpose. The masters can easily be moved, copied and converted without affecting the quality.

Concatenation loss

Your multi-track recorder probably has a number of file options and you might use a standard compact format such as MP3 for demos. Any format that compresses more than 50% is probably lossy. This means audio detail is lost when recordings are made and it can’t be recovered. Even when a full-size 16-bit CD is re-made from the compressed file it won’t sound the same as the original.

A problem arises when a lossy copy is compressed again. When a further copy is made using another compressed format (e.g. MP3 to MP3, or WMA to Ogg) the sound will be noticeably degraded. This is called concatenation loss and it gets worse as further compression of any kind is reapplied.

In theory a series of coding and decoding operations using the same codec would be transparent but this is rarely true in practice.

So remember the history of any copies and don’t double up any type of lossy compression unless you’re prepared to lose quality. Copies made over digital connections are usually OK because the data is normally mirrored, not re-compressed.

Format convertors

There are numerous audio file convertors available online and they work in various different ways. All are subject to concatenation loss and can’t make true digital copies of the original.

Uploading your downloads

All web hosts have some limit on bandwidth even if they say otherwise. I prefer a defined bandwidth agreement because your site is more likely to stay accessible and you’ll know if you can afford it when you get a peak. If you have a “no limit” account your site may be adversely affected by other sites on the same host (all hosts have a bandwidth ceiling).

Music download file sizes

Whatever format you choose for downloads there are several file size questions.

The chances of anyone downloading anything much over a megabyte, unless they know what it is, are slim. In practice a fast analogue modem takes 3 – 5 minutes to download a megabyte. Basic broadband is about ten times faster but even then small file sizes increase your chance of getting heard.

The common MP3 bit rate is 160kbps, although some people use higher rates. You can make smaller MP3s using mono (half the size obviously) and lower bit rates. For demos, I think 64kbps mono is fine, and the file size for a three minute number (about a megabyte) is as big as you want for an ad hoc download.

If you halve the size of your download files you also halve the bandwidth your visitors might use (although they probably won’t all log on at once new releases might cause peaks, and word of mouth can cause surges from time to time).

Bandwidth exhaustion can mean:

MP3 web server space

On a site like mine MP3 files occupy well over 95% of the server space. It’s worth knowing how many downloads you can keep before you need to buy more space—the formula is quite simple. It takes about a megabyte for every minute of good quality MP3 stereo (if you use mono you can double the number of files or length of time).

Download formats compared
TypeSize1 minuteExample
Uncompressedstereo100%10 MegabytesCD, WAV, AIFF
Compressed (lossless)stereo50%5 MegabytesFLAC, Apple Lossless
Compressed (lossy)stereo10%1 MegabyteOgg (Vorbis), WMA, MP3, AAC
mono5%0.5 Megabytes
 Lossy encoding at higher bit rates makes bigger files

You might find files on your host server take up more room than they do on your PC. This is because different size discs store files differently, so don’t make your calculations too tight.

Downloading or streaming?

I don’t think this is a real issue. It’s fairly easy to do either as long as your server supports streaming. Streaming isn’t really an option on a dial-up connection, but most players can be set-up to start playing downloads before they’re complete. The only application where streaming is necessary is radio-style programming; for individual tracks it doesn’t make much difference.

Online releases

Packaging and paperwork

Remember to fill out the artist, title and comments (e.g. copyright, web site, email) information for your MP3 tracks, and check that your jukebox or playlist software uses the (more or less) standard ID3v2 tags.

There is a place for ISRC codes in the MPEG file specifications, and in the ID3v2.3/4 specification (TSRC) but people normally use the ID3 comment (COMM) field instead. Retailers or aggregators will tell you how they want you to tag your tracks (often in the filename itself).

Other important aspects of releasing tracks and albums are covered on the CD release page. Most of this applies to download releases too.

Getting your tracks onto the Internet

There’s more about using ftp and getting online in Web sites, Your web site and Search engines. You can also use an aggregator to distribute your material online.

Download sites and aggregators

If you want to make downloads available through sites other than your own there are options in Digital distribution and Download sites.

Aggregators and download sites provide information packs telling you how to format and submit your tracks.

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