const int LUT_SIZE;
const int LUT[LUT_SIZE]; // waveform lookup table (typically 2^N, N >= 8)
Fixed index; // current index into LUT (integer + fraction)
Fixed delta; // delta controls output frequency
output_value = LUT[(int)index];
// NB: for higher quality use the fractional part of index to interpolate
// between LUT[(int)index] and LUT[(int)index + 1], rather than just
// truncating the index and using LUT[(int)index] only. Depends on both
// LUT_SIZE and required output quality.
index = (index + delta) % LUT_SIZE;
Note: to calculate delta for a given output frequency f and a sample rate Fs:
delta = FloatToFixed(LUT_SIZE * f / Fs);
You need to avoid discontinuities in the output waveform (these are the clicks you are hearing). The easiest way to do this is with a LUT-based waveform generator - this works for any periodic waveform (i.e. not just pure sine waves). Typically you use a fixed point phase accumulator, which is incremented for each new sample by a delta value which corresponds to the current output frequency. You can safely modify delta however you like and the waveform will still be continuous.
Pseudo code (for one output sample):
const int LUT_SIZE;
const int LUT[LUT_SIZE]; // waveform lookup table (typically 2^N, N >= 8)
Fixed index; // current index into LUT (integer + fraction)
Fixed delta; // delta controls output frequency
output_value = LUT[(int)index];
// NB: for higher quality use the fractional part of index to interpolate
// between LUT[(int)index] and LUT[(int)index + 1], rather than just
// truncating the index and using LUT[(int)index] only. Depends on both
// LUT_SIZE and required output quality.
index = (index + delta) % LUT_SIZE;
Note: to calculate delta for a given output frequency f and a sample rate Fs:
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评论（1）
您需要避免输出波形的不连续性（这些是您听到的喀哒声）。最简单的方法是使用基于 LUT 的波形发生器 - 这适用于任何周期波形（即不仅仅是纯正弦波）。通常，您使用定点相位累加器，该累加器对于每个新样本都会增加一个与当前输出频率相对应的增量值。您可以根据自己的喜好安全地修改增量，并且波形仍然是连续的。
伪代码（针对一个输出样本）：
Note: to calculate
deltafor a given output frequencyfand a sample rateFs:You need to avoid discontinuities in the output waveform (these are the clicks you are hearing). The easiest way to do this is with a LUT-based waveform generator - this works for any periodic waveform (i.e. not just pure sine waves). Typically you use a fixed point phase accumulator, which is incremented for each new sample by a delta value which corresponds to the current output frequency. You can safely modify delta however you like and the waveform will still be continuous.
Pseudo code (for one output sample):
Note: to calculate
deltafor a given output frequencyfand a sample rateFs: