Bit-Depth Converter controls

The following controls are located in the Bit-Depth Converter dialog.

Control

Description

Bit depth

Choose a setting to specify the number of bits that should be used to store each sample.

 

 

Dither

This control allows you to specify the randomness of the dither (generated noise) used to mask quantization

 

distortion resulting from conversion to a lower bit depth. You can select from several shapes, each roughly

 

describing the pattern that would be produced if you plotted a graph with the dither amplitude on the X-axis

 

and the probability of the dither values on the Y-axis.

 

As is frequently the case when working with audio, experimentation with dither values yields the best results;

 

however, keep the following information in mind:

 

• Half Rectangular Eliminates distortion resulting from conversion to a lower bit depth, but the noise level is

 

more likely to be dependent on the signal. This setting uses a maximum dither noise amplitude of 0.5 LSB

 

(least significant bit).

 

• Rectangular Identical to Half Rectangular, but with a maximum dither noise amplitude of 1 LSB (least

 

significant bit).

 

• Triangular Eliminates distortion products as well as any noise floor modulation, but results in a slightly higher

 

noise level. The option typically works well in conjunction with noise shaping.

 

• Highpass Triangular Behaves like triangular dither, but shifts its noise into higher frequencies. This is typically

 

the best option when used in conjunction with noise shaping.

 

• Gaussian Does not perform as well as Rectangular and Triangular dither, but may be suitable for certain

 

audio.

 

 

Noise shaping

Determines the aural positioning of quantization noise. Using this control, you can shift the noise into audio

 

registers that are less perceptible to human hearing. This lowers the perceived noise floor and creates the

 

illusion of cleaner audio.

 

High-pass contour noise shaping attempts to push all quantization noise and error into high frequencies.

 

Equal loudness contour noise shaping attempts to push the noise under an equal loudness-type of curve.

 

 

More

Click this button to view additional options that you can use to adjust your data window selection. For more

 

information, see Adjusting the data window selection on page 174.

 

 

Noise shaping dangers

Noise shaping places quantization noise near the audio’s Nyquist frequency, a value equal to one-half of the file’s sample rate. Consider the following information:

•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 the Noise shape control.

For this reason, we do not recommend using noise shaping on files with sample rates less than 44.1 kHz.

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