Free Your Music: How to Convert Digital Audio Files
Pages: 1, 2, 3

Recording Audio

Following are the basic steps for recording audio through your sound card in Windows. Mac users can get more tips in Five Fun Ways to Play with Audio Hijack Pro.

Figure 2. In Windows the mixer device might be a sound card or a program like Total Recorder that emulates a sound card. The Properties screen of the Volume Control program (above) allows you to switch between mixing devices if you have more than one installed.

1. In your recording program, create a new file and choose the sampling rate, resolution, and number of channels. For CD-quality audio, choose 44.1kHz, 16-bit, and stereo.

2. Launch the system mixer (Volume Control program).

   To access the Windows system mixer, double-click the speaker icon in the system tray. If the icon is not visible, you can launch the Volume Control program via the Start Menu, by selecting Programs → Accessories → Entertainment → Volume Control.

   When you launch the Windows Volume Control program, it defaults to the Playback Control screen. To adjust recording levels, select Options → Properties → Recording (see Figure 2). The screen with the recording controls should now appear (see Figure 3).

3. Select Digital, MP3/Wave, or Wave/Direct Sound as the source, depending on your sound card.

4. Play a sample of what you are going to record and set the recording level while watching the meters in the recording program (or the system mixer). Adjust the level-control sliders so the peaks stay below the red area (see Figure 4).

5. Queue up the source at the beginning of the track.

6. Click the Record button in the recording program, then begin playing the source.

7. When the source is finished playing, click the Stop button in the recording program.

8. Trim off any silence at the beginning or end of the track.

9. Save the audio to your hard disk in the desired format.

Figure 3. The Recording Control screen of the Windows Volume Control program allows you to select the audio source to record. To record audio from a jukebox program or internet radio stream, use Digital, MP3/Wave, or Wave/Direct Sound.

Figure 4. The level in the meter on the left is too low, with the peaks around –17dB. The level on the right is too high, with the peaks at 0dB, and clipping in both channels. The meter in the center shows optimum levels with peaks around –2dB.

Utility Programs

Table 3 lists several utility programs for capturing audio and converting files to different formats. Audio Hijack and Total Recorder are full-featured recording programs. BarbaBatch is focused on converting digital audio into a variety of formats. Wisecroft Ripper converts Real Audio to PCM WAV.

Legalities of Format Conversion

If you plan to convert files from a copy-protected format to an unprotected format, you have legal considerations in addition to technical considerations to contend with.

If you legally purchased the song, the Doctrine of Fair Use (a part of U.S. copyright law) allows you to convert the song to another format as long as you don't share it with other people. The Digital Millennium Copyright Act (DCMA) [PDF file] prohibits distribution of software designed to circumvent copy-protection measures, but does not explicitly prevent circumvention by individual users for Fair Use purposes.

Another issue is that the usage agreements of many online music stores appear to prohibit you from exercising your rights under Fair Use. The usage terms at the iTunes Music Store appear to allow conversion of copy-protected files to another format as long as it's for your own use, while the terms of stores that offer music in copy-protected WMA format (which includes most of the stores that sell major-label music) appear to specifically prohibit it.

While it is not against the law to convert copy-protected files you own to other formats, by some interpretations of the DMCA I would be violating the law simply by telling you how to do it. But if you own the original file and use the converted version solely for personal enjoyment, it's hard to see how you'd be doing any harm to the copyright owner. On the other hand, if you were to convert (or simply copy) copyrighted music and give it to someone else—for example, you convert a copy-protected song from an online music store to an unprotected MP3 file and give it to a friend—you would be committing copyright infringement.

Audio Examples

Following is a 30-second clip of Beethoven's Ninth Symphony recorded in several different formats to help you compare the effects of format conversion and data compression. [Ed. Note: Because there is no universal audio player, some of the links below may trigger a "missing plug-in" error message. QuickTime users can add Ogg Vorbis support with the free Xiph QuickTime Components and WMA support (for Macs) with Flip4Mac. Another way to hear all the files is to right- or Control-click the links to download them, then use a combination of stand-alone players. The open source VLC should handle everything but Real Audio. You can get an ad-free version of RealPlayer on the BBC site.]

• WAV (44.1kHz, 16-bit, uncompressed PCM) (5MB)
• MP3 (128kbps) (472KB)
• MP3 (64 kbps) (240KB)
• MP3PRO (64 kbps) (236KB)
• Ogg Vorbis Low Quality (64kbps) (256KB)
• AAC (64 kbps) (288KB)
• WMA (64 kbps) (252KB)
• Real Audio (64kbps) (256KB RA)
• Apple Lossless (600kbps) (2.1MB M4A)

Bruce Fries is a writer, technology consultant and entrepreneur, as well as an associate of the Audio Engineering Society, and founder of several high-tech companies.

Return to the digitalmedia.oreilly.com