Portable cordless telephone having an improved ringing device

A device for generating an acoustic signal from a digital input signal (in), said device comprising:

• a delay line (DL) for initially receiving N samples of the digital input signal, the value N being dependent on the fundamental frequency of the acoustic signal to be produced, for storing and delaying data values associated with the samples,
• an arithmetic unit (AU) for combining at least two delayed data values received from the delay line in order to form a modified data value, which is again stored in the delay line and delayed by the period N, the modified data values together also forming an output signal,
• up-sampling means (US) for calculating an up-sampling frequency on the basis of the fundamental frequency of the acoustic signal to be produced, on the basis of a sampling frequency at which the output signal is to be supplied, and on the basis of a maximum length of the delay line, the data being processed by the delay line and the arithmetic unit at the up-sampling frequency thus determined, and
• down-sampling means (DS) for down-sampling the output signal sampled at the up-sampling frequency (s[Few]) in order to supply an output signal sampled at the sampling frequency (s[Fe]) to an output unit (OU) adapted to produce the acoustic signal.

A method of processing a digital input signal (in) for generating an output signal (s[Fe]) to be converted into an acoustic signal, said method comprising:

• a step of storing (STO) data values associated with N samples of the digital input signal in a table, the value N being dependent on the fundamental frequency of the acoustic signal to be produced,
• a step of delaying (DEL) the data values stored in the table,
• a step of combining (COM) at least two delayed values from the table in order to form a modified data value, which is again stored in the table and delayed by the value N, the modified data values together also forming the output signal,
• a step of up-sampling (US), for calculating an up-sampling frequency on the basis of the fundamental frequency of the acoustic signal to be produced, on the basis of a sampling frequency at which the output signal is to be supplied, and on the basis of a maximum length of the table, processing of the data being effected by the storage and combination steps at the up-sampling frequency thus determined,
• a step of down-sampling (DS) the output signal sampled at the up-sampling frequency (s[Few]) in order to supply an output signal sampled at the sampling frequency (s[Fe]).