Numerically controlled oscillator: Difference between revisions

Revision as of 16:14, 21 January 2021

Revision as of 14:36, 13 February 2021

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Another related spurious generation method is the slight modulation due to the GRR outlined above. The amplitude of these spurs is low for large N and their frequency is generally too low to be detectable but they may cause issues for some applications.<ref name="Grzeg"/>

One way to reduce the truncation in the address lookup is to have several smaller lookup tables in parallel and use the upper bits to index into the tables and the lower bits to weigh them for linear or quadratic interpolation. Ie use a 24-bit phase accumulator to look up into two 16-bit LUTS. Address into the truncated 16 MSBs, and thatth 16 MSBs plus 1. Linearly interpolate using the 8 MSBsLSBs as weights. (One could instead use 3 LUTs instead and quadratically interpolate). This can result in decreased distortion for the same amount of memory at the cost of some multipliers.

===Amplitude truncation spurs===