As you play a digital music file on an audio-enabled device such as a computer or smart phone, the audio player displays information about the song. Sometimes that happens because the player has an associated database, sometime that happens because the information is embedded in the file. This blog is about embedding, how song information can be inserted into a special section of that audio file and become part of the file.

If you create your own digital recording – such as an interview or a band recording – and play the audio file on an audio-enabled device, the player might display only the name of the file and nothing more. That’s because the descriptive information is missing; there’s nothing to display. If you want the file to display information you have to add it in yourself.

Adding a description is easy to do. It is also a good practice if you intend to keep the file for a long time and want the file to be self-documenting and give you information about itself. Embedded information travels with the file.

Or rather, embedded information generally travels with the file. Audio files can also lose those descriptions as the files get copied, transferred from device to device or processed with different apps or software. But if you are aware of the potential issues, you can keep your text intact inside their host audio files. At the end of this post I’ll present a few experiments you can use to test audio files with embedded descriptions.

I mentioned the way some applications manage your sound collection with a database of information about the music it stores. These applications may display the title, artist and other information about the recording but all of that information comes from the database. These systems do not embed metadata into the individual audio files. There’s a big difference. And if you modify information about a recording while you are in one of these applications, you just modify database information; the information contained in the recording itself will not be affected.

MP3 metadata fields

Given the variety of digital audio files that exist, for this post we’ll just look at two of the most widely used formats: WAV and MP3. Of the two, WAV is the higher quality. More often than not, the audio it contains is uncompressed, which means that it remains exactly the same size as when it was recorded and it hasn’t been squished down into a smaller file size.

An MP3 is compressed, which means that some of the “less important” digital data – for example, frequencies that you probably couldn’t hear anyway – gets removed, which reduces the size of the file. The appeal of compression is that a smaller, compressed file transfers quickly over the Internet and between devices much quicker than a large file.

The added text information is called metadata and the process of adding descriptive text to an audio file is sometimes referred to as tagging. For more detailed information on embedding metadata you can consult the Federal Agencies Guideline titled “Embedding Metadata in Digital Audio Files.”

Header from an MP3 file

If you open a WAV or MP3 file with, say, a text editor such as SimpleText for Mac or Notepad for PC, you’ll see a dense mass of characters representing the audio data itself. But you’d also see — at the beginning or the end of the file — an area with plain English words describing the contents of the file. This is called the header and it is where the metadata resides.

Metadata field names in audio file headers are oriented to music recordings, even though the term “audio” includes spoken voice, and natural and human-made sounds. So audio metadata fields (sometimes called “frames”) have names like Artist, Song, Date and Genre, though there are many more field types available. In WAV files, these terms are represented by four-character codes, e.g., IART for artist, ICRD for creation date, and so on (there’s a list in the document cited above).

Let’s say you’ve recorded an interview and you want to add information about the recording to the audio file. There is plenty of software available for adding metadata but still, among all of the software, the metadata field names are pre-set with musical titles. So in your recording you could put the interviewee’s name as the Artist, give the Date of the recording and even title your interview session in the Song field. Better yet, most audio metadata fields include a comments field that can hold a lot of text. The field titles shouldn’t limit you.

To enter your own metadata and tags, you need the right tool. An online search will turn up many free WAV and MP3-tag editing tools that will open the audio file header and display a form into which you can fill in the information. For more advanced work there is music editing and processing software, which also prompts you to add metadata to the file when you save the file as a WAV or an MP3. Some audio processing software will even carry that same metadata forward; if you add metadata to a WAV file and then make an MP3 version from that WAV, the MP3 file will inherit the same metadata that you put into the WAV.

There is no single official metadata standard or container yet to which all audio software and hardware makers adhere, though the closest thing is a popular informal container called ID3, which is most often associated with MP3s. An online search for “ID3 tag tool” will turn up a lot of free and useful tools that’ll enable you to see and edit the headers of MP3 files. For more detailed information about ID3, see the Library of Congress’s Sustainability of Digital Formats site for “ID3 Metadata for MP3, Version 2.”

If you sell or distribute your music online in the form of MP3s, adding Genre information can be as important — maybe even more important — than Name or Title, since many people often shop for songs of certain genres. And if you upload your file to a commercial distribution service, the metadata in your files should get sucked right into their system. Such metadata can be crucial for a musician’s livelihood, particularly regarding copyright and contact information. Musicians might also want to register an ISNI number, a unique ID sort of like a social security number, and add their ISNI number into their music files with the other metadata.

Audio metadata is not only good for documenting and displaying information about an audio file. When the file gets indexed, the English words in the header become searchable. So packing an audio header with rich metadata is a good way to attract searchers to your music.

The header/metadata system is not 100% reliable. It is possible for metadata to get ignored when an audio file is copied or stripped out if an audio file is processed, modified or altered in some way. The most reliable means of preserving metadata is to add it to the original file, the master file (ideally an uncompressed WAV), and store the master file safely away. Only work with copies. And check the copies to make sure they, too, contain the metadata. You may have to add it in again.

Until standards are in place and automatically implemented by all the appropriate audio hardware and software companies, it is especially important to be mindful of audio metadata if you intend to preserve audio files that you’ve created yourself or are responsible for or have some financial stake in.

So, on to the experiments. Here is a song from the American Memory collection, “John Henry,” sung by Arthur Bell . Download the MP3 version and the WAV version (on a PC: right click and “save link as”; on a Mac: control click and “save link as”) and run some tests on them.

TEST #1 – DISPLAYING METADATA

• Run whatever media player you use to play music on your computer and open up the MP3 file. As the song plays, does any song information display? You might try browsing the menus for Summary or Properties. Try different players. Try the same thing with the WAV file.
•  Import the MP3 and WAV files into your smart phone or other listening device. Does the song information display for both files?
• Using a text editor (such as TextEdit on a Mac or NotePad on a PC), open the MP3 and WAV files; the WAV file is large and will take a while to display. Make sure your text editor is set to open “Files of type > All files” or it won’t see either audio file. Can you see any English words at the beginning or end of the contents? That’s the header.

TEST #2 – MODIFYING MP3 METADATA

• Search online for “ID3 tagger.” Once you find one, download and install it.
• Run the ID3 tagger and open the MP3 file. The metadata should display in several fields. Change the information in any field — type in anything — then close it up and play the newly modified MP3 file with a media player. Does your new information display in the player?

TEST #3 – DOES MODIFYING THE AUDIO FILE AFFECT THE DESCRIPTIONS?

• For this you will need audio processing software. If you don’t already have it, search online for “audio processing software.” SourceForge.net usually has free, open source, cross-platform software for recording and editing sounds.
• Once you have the audio processing software running, open the WAV and MP3 files and modify the WAV a little. Snip out the hiss in the first six seconds of the file. Maybe reduce the bit rate or convert it from mono to stereo. Then close the file and play it with a media player. Does the metadata still display?

If you try any of these experiments, please let us know what software or hardware you used and what your results were.