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Preparing Audio for the Internet with Sound Forge
Written by Scott R. Garrigus - 2005, Cengage Learning. Reprinted with Permission.
This article is an excerpt from the following books: The Sony Sound Forge Power! Books Series

Preparing Audio for the Internet with Sound Forge
In addition to video files, I also talked about how to save audio files in the RealAudio, MP3, and Windows Media formats in Chapter 4. But I didn't talk about how to actually process your files before saving them to these formats. Because the RealAudio, MP3, and Windows Media formats all use compression to reduce the size of audio data so that it's easier to download over the Internet, they can affect the sound of your audio. Be sure to have a reliable broadband internet connection for fast downloads. You can compensate for these unwanted changes in quality by following a few simple processing procedures before you convert your files.

Remove DC Offset
As I mentioned in Chapter 8, it's always a good idea to remove any DC offset that may be present in your audio data before doing any processing. Otherwise, you can add unwanted anomalies. To remove DC offset:

1. Select all the data in your audio file by choosing Edit > Select All (or pressing Ctrl + A on your computer keyboard).
2. Choose Process > DC Offset to open the DC Offset dialog box.
3. Choose the Remove DC Offset (Scan Entire Sound File) Preset.
4. Click OK.

Apply Equalization
Equalize your file while keeping in mind that most of the high-end and extreme low-end content might be lost when you save the file to one of the compressed file formats. It may take some experimentation, but cutting the low frequencies (below 60 Hz) and the high frequencies (above 10 kHz) is a good place to start. This helps in reducing any of the anomalies that can occur during the file format compression. To compensate for the frequencies being cut, you can boost some of the low frequencies that are still intact around 200 Hz. You can also boost the mid-range frequencies around 2.5 kHz. This emphasizes the more important content in your audio, such as vocals, if there are any. What's great about Sound Forge is that it accomplishes all of this equalization with one process. Here's how it's done:

1. Select all the data in your audio file by choosing Edit > Select All (or pressing Ctrl + A on your computer keyboard).
2. Choose Process > EQ > Paragraphic to open the Paragraphic EQ dialog box.
3. Activate the Enable Low-Shelf option. Set its frequency to 60 Hz. Then set its gain to -Inf. Doing this cuts out any frequencies below 60 Hz, as I mentioned earlier.
4. Activate the Enable High-Shelf option. Set its frequency to 10,000 Hz. Then set its gain to -Inf. Doing this cuts out any frequencies above 10 kHz, as I mentioned earlier.
5. Set the gain on the first parametric band to +3.0 dB. Then set its Center Frequency to 200 Hz. This boosts the low frequencies around 200 Hz. You can experiment with how much the frequencies are boosted, but I wouldn't go any higher than +6.0 dB. Also, set the Width to 1.0.
6. Set the gain on the second parametric band to +3.0 dB. Then set its Center Frequency to 2,500 Hz. This boosts the mid-range frequencies around 2,500 Hz. You can experiment with how much the frequencies are boosted, but I wouldn't go any higher than +6.0 dB. Also, set the Width to 1.0.
7. Leave all the other parameters set to their defaults.
8. Click the Preview button to audition your file before making any changes. If you hear any clipping or distortion, try lowering the gain on one or both of the parametric bands.
9. Click OK.

Apply Dynamic Processing
In addition to altering the frequency content of your audio, converting to RealAudio, MP3, or Windows Media can reduce the dynamic (amplitude) range, making your audio sound flat or dull. Adding a bit of dynamic processing before conversion gives you some control over your final signal levels, rather than leaving them to chance. To accomplish this, you need to use Sound Forge's Graphic Dynamics function:

1. Select all the data in your audio file by choosing Edit > Select All (or pressing Ctrl + A on your computer keyboard).
2. Choose Effects Dynamics Graphic to open the Graphic Dynamics dialog box.
3. Choose the 2:1 Compression Starting At -18 dB Preset. You can experiment with the Ratio parameter if you want. A good ratio range is between 2:1 and 4:1, but it may vary with some audio material, so you have to use your own judgment. But be careful, because too much dynamic processing can add unwanted artifacts and make your audio sound dull and lifeless.
4. Click the Preview button to audition your file before making any changes. If you hear any clipping or distortion, try lowering the Output Gain parameter.
5. Click OK.

Normalize
The last step is to normalize your audio. As I talked about in Chapter 8, normalization raises the amplitude of an audio signal as high as it can go without causing clipping or distortion. This guarantees that your file uses the maximum amount of digital resolution and amplitude available. It also ensures that you use the highest possible volume when converting your file for the Internet, which helps in masking low-level noise and possible compression artifacts. To accomplish this, use Sound Forge's Normalize function:

1. Select all the data in your audio file by choosing Edit > Select All (or pressing Ctrl + A on your computer keyboard).
2. Choose Process Normalize to open the Normalize dialog box.
3. Choose the Maximize Peak Value Preset.
4. Click the Scan Levels button to find the highest amplitude level in your audio data.
5. Set the Normalize To parameter to anywhere between -0.50 dB and -1 dB. In this case, you don't want to normalize to 0 dB (or 100 percent) because the RealAudio, MP3, and Windows Media conversion processes don't always handle 0 dB signals very well. They can sometimes "choke" on such a high amplitude signal, so it's best to leave a small amount of dynamic room for the conversion process to work its magic.
6. Click the Preview button to audition your file before making any changes. If you hear any clipping or distortion, try lowering the Normalize To parameter.
7. Click OK.

Now, your file is ready to be converted to RealAudio, MP3, or Windows Media (see Chapter 4).

For more information: The Sony Sound Forge Power! Books Series


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