All Is Not Lost

Oct 1, 2006 12:00 PM, By Vijith Assar

           

Chances are you occasionally send rough mixes to clients or vie for jobs using compressed audio samples. But it's surprising how little some engineers and producers know about audio-compression techniques, especially considering that their art and their livelihoods can depend on them. Each of the available formats has unique strengths and weaknesses, and selecting the one that suits your needs is the Internet equivalent of choosing the right microphone or reverb.

FIG. 1: Both ID3v1 and ID3v2 tags can coexist for the same file. The two types can even contain different information.

Smart encoding practices can result in better-sounding files that can more accurately present your abilities to potential clients. They might even win you a contract over a competitor who just coasts along using a program's default settings. What's more, compatibility issues can arise from blindly using default compression methods; many programs subtly encourage you to use their native formats. Being careful about your choices can ensure that potential customers are able to listen to your clips.

I Can See Clearly Now

Numerous lossy audio encoders have emerged in the past few years, all of which are trying to beat the ubiquitous MP3 by offering sonic and technical advantages. Though each offers its own feature set and underlying technologies, what they all have in common is the goal of perceptual transparency.

Perceptual transparency is based on the idea that there is a certain threshold beyond which higher sound quality becomes largely inaudible and, as a result, functionally useless. This threshold will vary depending on the listener: EM readers probably have a higher average threshold than most consumers. When properly executed, lossy compression is tailored to the intended listener and will compress just enough so that any artifacts created lie barely outside the limits of audibility. That's precisely why MP3 files became so widespread: most people who were not expert listeners found that the audible artifacts from even relatively bad MP3s, such as those created at low bit rates by inferior first-generation encoders like Fraunhofer and Blade, were not troublesome enough to derail their listening experience. As a result, consumer adoption of the MP3 format spread quickly.

Tag, You're It!

But perceptual transparency is not the only goal. Every modern compressed audio format includes provisions for storing metadata, or data about data. Metadata is information about the music — artist, song title, album name, and so on. It's possible to accomplish the same thing using file names (“The Beatles - 1968 - The White Album - Side 3 of 4 - Track 4 of 7 - Everybody's Got Something to Hide Except Me and My Monkey.mp3,” for example), but there are programs that can read metadata and apply it to file names and directory structures across a large audio collection with a single click. That makes metadata infinitely more powerful than file names, because it allows you to reorganize your collection on a whim.

The ID3 standard emerged in the mid-1990s as a way of organizing metadata in a tag, which is a block of text attached to the audio file. This tag is arranged to make its contents easily readable by any program or hardware device accessing the file. It's prudent to set up your tags carefully, because they are an opportunity for you to achieve name recognition with clients and to ensure that you get proper credit for your work. Tagging is as easy as choosing Edit Info (or the comparable option) from the contextual menu in your MP3 playback program and filling in the data fields that appear.

The first iteration of the MP3 tag, ID3v1, was limited to 128 bytes of text, which meant that fields were sometimes too short for the data that belonged in them. ID3v2 solved this problem, but because the v2 tag is placed at the beginning of the file (rather than at the end as in v1), the process of tag writing can be slower. These days, most people use some form of ID3v2 (there are several subvariants), but it can't hurt to include both ID3v1 and ID3v2, especially because you never know which tag type your listeners' playback systems might be reading (see Fig. 1). If you have included only ID3v2 tags and your listeners have their programs or hardware set to read ID3v1, you'll show up as “Unknown Artist.”

Any Comments?

Because the Comment field in ID3v2 is infinitely extensible, it can be used to store fairly advanced information. iTunes stores volume-normalization information (Sound Check values) in a special frame within the Comment field, and several programs can embed pictures of an album cover there. The Comment field is one of the most powerful tools available, because it's searchable and easily accessible by all major programs. If you're sending the files over the Internet, for example, you can use comments to plug your studio (be sure to include contact information). If you plan to use the files internally, why not store a list of the session players used on each track, complete with phone numbers in case you need to call them again for a similar project? You can also use it to make notes about alternate arrangements or mixes or mastering jobs, or rough recall information, or even outstanding unpaid balances from clients. The possibilities are endless.

ID3v2 also includes a URL field in which you can specify a Web address; this is advisable because you never know when one of your tracks might fall into the hands of a major record-label executive or a potential client. The field is not readily accessible from iTunes, but there are a slew of programs that can access it from Windows, and Panic Audion (see the sidebar “Manufacturer Contacts” for a list of companies mentioned in this article) is a lightweight iTunes alternative for Mac OS X that provides easy access to the field. It's also wise to include the URL in the Comment field in case your eventual recipient is an iTunes user.

Although it is both useful and widespread, ID3 is a tag format that applies only to MP3 files. There are a few rogue programs that might occasionally try to force ID3 tags onto file formats that don't actually support them, such as WAV. This practice should be avoided, though, because it invariably violates the standard of the file type being mangled, leaving you with a nonstandard and possibly unplayable file. Instead, you should use the metadata format native to the file type you choose. There are as many tag varieties as there are audio formats, but with proper decoder implementation, the differences between them should be imperceptible to the end user.

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