Digital versus analog levels

When recording to an analog medium such as magnetic tape, recording engineers typically try to keep VU (volume unit) meters as close to zero as possible. This ensures a high signal-to-noise ratio while preserving adequate headroom to keep the tape from saturating and distorting. In addition, occasional peaks above 0 do not cause problems because the tape saturation point is not an absolute.

However, this is not true in the digital realm, where amplitudes are stored as discrete numbers instead of continuous variables. The flexible recording ceiling of analog is replaced by the absolute maximum sample values of digital audio. Stored signals must never have a value above these maximums, as the wave peaks are literally clipped. This clipping adds audible distortion and though it can go unnoticed, it can also ruin an entire project. Therefore, sample with the understanding that digital audio has absolutely no headroom.

Setting digital audio levels

Because digital audio has no headroom, setting the sampling level becomes critical. If the loudest section of the audio is identified in advance, the recording level should be set so that the peak is as close to 0 dB as possible to maximize the dynamic range of the digital medium. If the loudest section of audio is unknown, allow 3 to 6 dB of headroom for unexpected peaks.

Tip: From the Tools menu, choose Find and use the Find dialog to identify the largest peak in your file.

Using the channel meters

From the View menu, choose Channel Meters to open or close the channel meters. By default, Sound Forge software provides peak meters that you can use to monitor your audio levels. You can also choose to display VU/PPM (peak program) meters, a phase scope, and a mono-compatibility meter.

The peak meters display instantaneous levels during playback to help you determine the loudest level in your audio signal and whether the signal is clipping.

To prevent clipping, keep an eye on your peak meters. Peak levels should never exceed 0 dB. You can use the Status tab in the Preferences dialog to calibrate the VU/PPM meters to their associated levels on the peak meters and adjust the VU meters’ sensitivity.

Mono-compatibility meter

Phase scope

Peak meter

VU/PPM Meters

Showing or hiding the Channel Meters window

From the View menu, choose Channel Meters to open or close the channel meters window. You can dock the Channel Meters window on any edge of the Sound Forge workspace.

44 CHAPTER 2