86
Noise shaping dangers
Noise shaping places quantization noise near the audio’s Nyquist frequency, a value equal to
•A file with a sample rate of 44.1 kHz has a Nyquist frequency of 22.05 kHz (at the high end of human hearing). Applying noise shaping to this file results in audio perceived to be cleaner than it actually is.
•A file with a sample rate of 22 kHz has a Nyquist frequency of 11 kHz (well within the sensitive range of human hearing). Applying noise shaping to this file results in audio that is perceived to be noisier than it actually is. Ironically, this defeats the entire purpose of noise shaping.
For this reason, we do not recommend using noise shaping on files with sample rates less than 44.1 kHz.
Minimizing quantization errorThere are at least three methods of minimizing quantization error when decreasing a file’s bit depth: noise gating, compression, and normalization.
Noise gating
Frequently,
1.From the Effects menu, choose Noise Gate. The Noise Gate dialog appears.
Specify a noise gate
2.Choose a noise gate preset from the Preset
Compressing
Decreasing the dynamic range of a sound file makes it easier to represent with decreased bit depth.
1.For users of the full version of Sound Forge: from the Effects menu, choose Dynamics, and choose
Graphic from the submenu. The Graphic Dynamics dialog appears.
For users of Screenblast Sound Forge: from the Effects menu, choose Dynamics. The Dynamics dialog appears.
2.Choose a preset with a small amount of compression (2:1 or less) from the Preset
OK.
CHANGING FILE ATTRIBUTES AND FORMATS | CHP. 6 |