Method for removing aliasing in wave table based synthesisers
AssigneeTelefonaktiebolaget LM Ericsson (publ)
InventorsUlf Lindgren, Alberto Jimenez Feltstrom, Thomas Jacobsson
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Abstract
A method and apparatus are provided for changing the pitch of a tabulated waveform in wavetable based synthesizers. Harmonics that normally would be aliased before a transposition process are removed by a discrete time low pass filter at the same time that the tabulated waveform is reconstruction and resampling.
Claims12
A method of processing a first discrete time signal, x[n], to generate a second discrete time signal, y[m], wherein the signal x[n] comprises a sequence of values that corresponds to a set of sample points obtained by sampling a continuous time signal x(t) at successive time intervals Ts, the method comprising:
- generating a sequence of values, each of the values corresponding to a respective m of the second discrete time signal y[m], wherein each of the generated values is based on a value obtained by a convolution of the first discrete time signal x[n] with a sequence representing a discrete time low pass filter having a length based on a predetermined window length parameter L, the convolution being evaluated at one of successively incremented phase increment values multiplied by the sampling interval Ts and corresponding to a respective m value.
An apparatus for processing a first discrete time signal, x[n], to generate a second discrete time signal, y[m], wherein the signal x[n] comprises a sequence of values that corresponds to a set of sample points obtained by sampling a continuous time signal x(t) at successive time intervals Ts, the apparatus comprising:
- logic that generates a sequence of values, each of the values corresponding to a respective m of the second discrete time signal y[m], wherein each of the generated values is based on a value obtained by a convolution of the first discrete time signal x[n] with a sequence representing a discrete time low pass filter having a length based on a predetermined window length parameter L, the convolution being evaluated at one of successively incremented phase increment values multiplied by the sampling interval Ts and corresponding to a respective m value.
Dependencies are inferred from the claim text.