Audio is the least time-consuming way to prepare non-written media for a class, whether it’s to create quick notes on a subject, an interview (audio is, by far, the easiest and most efficient way to interview someone for dissemination), a podcast, music, or what have you. It’s also one of the least expensive, usually only requiring a ~$15 microphone and a free copy of Audacity for recording/editing.
Also, unlike video, there is a refreshing simplicity to recommending file formats when it comes to audio. As always, it all depends on what you want to use it for, although plenty of people skip most of what’s written below and work entirely in the MP3 format. And there’s nothing wrong with that.
But what are the other formats used for?
I am recording and editing sound on one computer
When recording and editing on a computer, you’ll typically be using an uncompressed audio format, usually WAV or AIFF, and take up roughly 10MB of disk space per minute. This is your highest quality digital audio and the best for editing and listening to, but not good for mobility or storing your collection of 2,000 audio CDs onto your hard disk. Unlike video, though, it’s quite easy to move this high-quality audio to different computers given a blank CD (able to hold 80 mins of such audio)/DVD or memory stick. It’s not what you’d be uploading for class use, however.
I am recording and editing sound on many computers/collaboratively
Honestly, you could use the formats above, or even on MP3s (see below), but there’s another category of audio files you could consider. Lossless formats like FLAC, ALAC, or APE work just like .zip files on a computer. These formats compress the audio so they only take up, say, 5MB of disk space per minute, but uncompress to full quality when used/played. If you want to work with high-quality audio, but you’re emailing your audio files back and forth with a collaborator, this type of format is a great choice.
I want to share my audio recording with others by handing them copies
Well, this is what audio CDs were created for. You typically won’t export directly to CD, and will instead export as something else (MP3 if quality doesn’t have to be great, otherwise a lossless format like WAV or AIFF). You can then use that format to build a playlist in a program like iTunes (what I tend to use) and let that program burn the CD disk for you.
Time for a little background here (feel free to skip to the next section if you don’t want to get any nerd on you): Audio CDs use a file format called PCM (“pulse-code modulation” was created back in 1937, believe it or not). Since PCM was first suggested, digital sound formats typically work on its two principles: sample rate and bit depth.
Sample rate works not too differently from Frames Per Second (FPS) in video; video captured at 12 FPS (as you get off older cell phones or cameras) looks very jerky and stuttering, whereas watching a movie in a theater recorded at 29.97 FPS fools our eyes into thinking that there’s actual motion going on and not a quick series of cleverly recorded still images. Sample Rate for audio is measured in the thousands of hertz (kHz). The higher the kHz, the more frames/samples of audio per second are captured, and the “smoother” the audio appears to be. Telephone systems and devices like walkie-talkies use a 8 kHz signal (which is why holding up a phone to a stereo speaker so someone can listen in on the other end tends not to work very well—it’s considered acceptable for voice, though). An audio CD’s sample rate is 44.1 kHz. The range of human hearing, by comparison, is between 20 Hz and 20 kHz. So 44.1 kHz might seem like overkill…
Bit depth is how accurately each of the samples is captured. To simplify, high bit depths can capture very soft to very loud noises (their dynamic range) much better than lower bit depths. CD Audio is 16-bit, allowing for a dynamic range of 96 dB. If you recorded a symphony at 2-bit, by comparison, you’d only have a dynamic range of roughly 12 dB, meaning that the soft instruments would sound relatively close to the loud instruments and the whole thing would sound “flat,” no matter what your sample rate was.
(Most programs let you set these values when you save an audio file, and now you hopefully have a better idea of what they’re talking about.)
I want to share my audio with people on the internet
This is probably the easiest one to answer, and the most common use for digital audio files nowadays. The MP3 format is by far the most popular format, though Apple users might see the AAC file format more often. Both these formats are “lossy,” which means they’re compressed and never as good as the formats above, but most people can’t tell any significant difference in quality. What’s important with these formats is their bit rate (not bit depth). Lower bit rates result in smaller files but not great quality; higher bit rates result in larger files that result in corresponding higher quality. AM radio is analogous to 32 kbit/s, FM to roughly 96, 192 is the highest you can usually copy audio CDs to MP3 format, and 224 – 320 kbit/s is the highest range. Audacity’s default MP3 will export at 128, which is fine for most any purpose. Such MP3s can be posted online with very little trouble in terms of file size or user difficulty.
I want to share my audio with others, but I want to make sure they can’t steal it
The truth is, the best you can do is make it more difficult for people to steal the information you place online (usually more accurately: “take for their own use”), but you can’t 100% prevent it. This includes anything you put online for group consumption. What you can do, however, is make sure you sign your work. MP3s, for instance, are very easy to meta-tag. When you save an MP3 from Audacity, or use the Get Info command on a track inside iTunes, you can put a lot of data inside the file, including title, author, website, general notes, and other information. This data is not only how music players know what to display in the play menu, but how a person who came across the audio file can get information on how to contact the author.
As far as help or advice on recording sound, I can be contacted at CTLT and am always happy to help. Greg Maier – gmmaier@ilstu.edu – 438-2327
