Creating an Audio File or Data CD Master

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Many times in commercial production, regular audio CDs will be used to transfer mixes to and from video post houses , allow clients to make approvals , and even to deliver masters to radio broadcasters. CD-Rs can be used to transfer any data format between editors or facilities. Data files can even be delivered via the Internet over FTP connections. Email works for MP3 files.

There are so many ways to deliver digital media in data format that the industry could possibly see the end of tape machines altogether. The advent of cheap CD-R media and burners allows you to move large amount of audio between places without the need for reels of tape. Even the new iPod, with 30 and 40 Gigabyte models available, is a terrific way to take your Pro Tools session to another studio .

When creating these data files that are, in essence, your master tapes, you must take into consideration factors such as synchronization, sample rates, and file formats.

Redbook Audio CDs

While it is not preferable due to sample rate conversion to 44.1kHz, Redbook audio CDs can be an alternative method for creating stereo master recordings of your work. Make sure to include two beeps for synchronization, as audio CDs cannot support time code.

It is even possible to put a complete 5.1 Surround stereo mix onto a Redbook audio CD for trasfer to another playback system the way to do this is to record pairs of channels as individual tracks on the CD. Each track on the CD will have a 2-beep at the beginning to allow synchronization in another workstation. You could pair left and right channels, center and LFE channels, and the surround channels, each pair on a track of the CD. When bouncing these files, be sure to maintain the exact same selection so the files can be lined up sample accurately later. This is certainly not the preferable way of doing things, but it will work in a pinch . Be aware that typical video workstations are set up to import audio from Redbook CDs at the fastest and lowest quality available. If an analog transfer from the CD is used, calibration issues arise. Try to avoid the use of audio CDs as a method of transfer unless absolutely necessary.

Preparing Audio Files for Internet Streaming

Preparation of mix files for Internet use usually requires using a higher reference level. As with music recording, the Internet does not have a standard reference level. As most files that will be used on the Internet are going to be data compressed, a higher reference level should work better. It has been my experience that lossy data compression used for Internet streaming sounds better when starting with a file that is as loud as possible. This goes against the grain of preserving the highest fidelity, but often the softer mixes don't translate very well once they have been compressed by an algorithm such as MP3. You should experiment with each codec to find the combination of settings and levels that yield the highest quality.

Another thing to consider is the environment in which people will listen to this mix. Small multimedia speakers placed close to a CRT monitor and a loud whining desktop computer do not make for an ideal listening environment. Reducing the dynamic range to fit this limited playback scenario can work well.

QuickTime provides its own Internet streaming compression for video files bound for the web. The web designer will make the choices concerning audio compression here, as the compression type depends on the available bandwidth and video data rate as well. Try to obtain a copy of the finished file in order to check the content creator's work. It is not uncommon to find that your mix has been horribly mutilated by data compression. You might want to speak with the programmer to find out what compression was used and if there's a way to improve the situation.

If the end file is to be an MP3, try to do the encoding yourself to ensure quality. Applications such as Peak can encode MP3 files in a high-quality fashion, as shown in Figure 9.6. Consumer MP3 encoders tend to sacrifice quality for speed. Be wary of them. Apple's iTunes tends to sound pretty good, however.

Figure 9.6. The export dialog box in Peak showing options for MP3 encoding. 128Kbytes should be the minimum bit rate used to encode MP3 files that retain any decent fidelity.

If you know your mix file is destined to be encoded into a Flash file for the Internet, send the programmer a Redbook audio CD. The Flash program will encode your audio file into an MP3 format that is embedded within the Flash file. Sending an already encoded MP3 does not help in this case.

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