3.8-- Using the dither options

Whenever the output bit-depth is smaller than the input bit-depth a downward re-quantization is implied and it is recommended to apply "dither" to avoid audible non-linear distortion - especially for low bit-depths. ReSample provides a full range of dither options via the selection dialog (either for the default new task settings or for the selected task(s) settings, as determined by the toggle state of the settings panel). See appendix 5.3 for a full discussion of dither and a detailed description the algorithms implemented in ReSample.

Although dither is normally used only when the bit-depth is reduced, ReSample allows complete flexibility to apply dither to any conversion task, irrespective of the bit-depths in question. Possible dither options are:

Dither method	Notes
None	No dither applied.
Rect	Rectangular "additive" dither applied. See appendix 5.3.2.
Tri	Triangular "additive" dither applied. See appendix 5.3.3.
1st-order	First-order "high-pass" noise-shaping. See appendix 5.3.4.
FIR	Arbitrary FIR noise-shaping. See appendix 5.3.4.

3.8.1--- Importing user-defined FIR noise-shaping filters
When the FIR dither method is selected, the "Filter" button appears. This can be used to activate the FIR-filter-selection window (as shown below) where a choice can be made from a selection of built-in noise-shaping filters (designed for 44.1 kHz only), or from a user-defined filter via an imported ASCII file.

Figure 11 Configuration settings window for selecting the FIR filter for use with the "FIR" noise-shaping dither option.

The format of the ASCII file is straightforward, as summarized in the table below.

Table 1 ASCII file structure for storing FIR filter coefficients readable by ReSample

Line number	Entry	Notes
1	RESAMPLE_FIR_NOISESHAPER	Description of the filter type (string variable type).
2	N	Length of the FIR filter (integer variable type).
3 to N+2	B(1) to B(N)	Filter coefficients (double variable type).

An example of such a filter file is "noiseshape.txt" located in the "NoiseShapingFilters" subdirectory of the ReSample root installation directory. The file listing is as follows:

RESAMPLE_FIR_NOISESHAPER 5 2.033 -2.165 1.959 -1.590 0.6149

Note that ReSample can also read any ASCII filter file exported from Sounds Logical's WaveWarp application. The filter file format is identical except for the name in the header: WW_FILTER_FIR instead of RESAMPLE_FIR_NOISESHAPER. ReSample recognizes both.