Squeezing Sound

With all the buzz about Internet video, YouTube and video sharing in general, it would be easy to forget about audio on the Internet.

I guess in the minds of some, audio had its day, and they’ve moved on to video. Not so fast! Streaming audio, MP3s and other compressed audio sources are everywhere on the Internet, bigger and better than ever before. Using a little imagination and tools you already have, it’s easy to leverage the power of audio on the Internet. Spend the next few minutes here, and you’ll be squeezing sound like a pro.

Tech Talk

Uncompressed audio files are big. The average song ripped from a CD is 30-50MB. While it’s possible to post a monster file like that to the Internet, it would take quite a while to download, making it completely impractical for most purposes. That’s where audio compression comes in. Using a combination of psychoacoustics, math and a little bit of magic, we can easily squeeze large audio files to a tenth of their original size or smaller. Of course, there is a trade off in quality – compressed audio files are “lossy” and don’t sound exactly like the original.

There are several types of compressed audio – AAC, MP3, Windows Media, Ogg Vorbis – and each has its own way of squeezing sound. But in general, they all go through similar processes. They analyze incoming audio for content, and compare this profile to models based on human hearing – what we hear and how we hear it. Then, the encoder decides which elements to eliminate. First to go are extreme highs and lows. Next are softer sounds that will be masked by louder ones. This continues until we have a compressed audio file. Another important decision is the bitrate. For near-CD-quality music, a bitrate of 128KB is a standard minimum. For voice, the bitrate can go much lower. Many syndicated talk shows stream their voice broadcasts around 48KB, a compromise that won’t seriously degrade audio quality. If you’re a complete geek and want to know even more, Wikipedia has an excellent article on audio compression. For the rest of us, the general rule is: the harder you squeeze, the smaller the file and the worse it sounds.


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Audio on a Diet

There are many different ways to convert compressed audio files. Probably the easiest is to load the file into iTunes and choose the Convert Selection to MP3 option. As an alternative, most audio editing applications include compressed audio options in their Save As functions. Audition, Sound Forge, Audacity and even Reaper support multiple compression formats and bitrates. Alternatively, you can use a standalone freeware program like CDex to perform audio file compression.

People love to debate the sound quality of compressed audio formats. While methods and features differ among the various types, the simple fact is they all sound pretty good today. When you save a compressed audio file, there are several options to consider. We’ve already touched on bitrate: the higher, the better. There is also the question of mono or stereo. In a stereo file, the bits are divided between the two channels; a 128KB stereo file is essentially two 64KB channels. If you don’t specifically need stereo, encode the clip as mono, and you’ll get a free quality bump. You may also have the option of specifying sampling rate. For this, stick with the CD standard of 44,100Hz or the video standard of 48,000Hz.

Most compressed audio formats also allow the attachment of other information and graphics. In the MP3 format, this information is included in the ID3 tag – Windows Media calls it Meta Data. Information can include the title, artist, year, etc. You can also attach a JPEG or other small image to the file for identification purposes. In some formats, you can also include cue points that will launch a browser window and visit a specific Web site or HTML file. This option alone offers several untapped possibilities. Let your mind wander.

Upload, Download

We’ve looked at the concepts and techniques used to create compressed audio files, but what can you do with them? Try these options on for size. Since 2008 is an election year, many media producers will be creating content for candidates. Compressed Internet audio is useful for speech podcasts, recorded interviews and radio commercials. You can also make an assortment of official sound bites available to the media in the press section of the Web site.

Musicians can benefit from compressed audio. First, e-mailing MP3s to band mates can simplify rehearsal and collaboration. You can upload MP3s to your Web site or MySpace page and stream sample recordings for the visitors. Use compressed audio for online promotional packs and e-mails to venue managers for potential bookings.

I haven’t forgotten you, the humble video producer. Consider using compressed audio files when shopping for vocal talent. You can e-mail a script to a voiceover specialist, who can record, compress and e-mail you a finished track. Make sure to use higher bitrates for this type of application. You can also leverage compressed audio for approval on soundtrack music and finished audio tracks. Compress a copy and e-mail to the client. It saves time, trouble and blank CDs. If you produce audio projects on a regular basis, don’t forget to post samples to your Web site – sort of a virtual demo tape.

It’s Your Turn

You see, there is still a place for audio on the Internet. The tools and tech are well established and integrated into applications you already use. While you may not need these techniques every day, it’s nice to have them in your bag of tricks when the client calls. If your entire experience with compressed audio is telling iTunes to rip a CD for your music collection, you’ve got some experimenting to do. Try different bitrates and compression methods, and make your own evaluations. Give it a good squeeze.

Contributing Editor Hal Robertson is a digital media producer and technology consultant.

Sidebar: Standards, Please

How many times have you visited a Web site, hoping to watch or listen to some media, only to find that you need to install some off-the-wall codec (and its bloated software bundle) for playback? The only codecs your browser should need are Flash, QuickTime, Shockwave and Windows Media. Let’s face it, MP3 is the compressed audio standard, and it doesn’t take anything special to play it in a browser. If you’re going to the trouble of encoding audio for a Web site or download, make it easy on your listeners and use a standard format.

The Videomaker Editors are dedicated to bringing you the information you need to produce and share better video.