Method for operating a hearing device and hearing device
A hearing device comprises a receiver, an input buffer and a sample processor, the receiver being adapted to receive samples of a digital audio signal and feed received samples as a digital input signal to the input buffer, the sample processor being adapted to process the buffered samples to provide samples of a digital output signal such that the digital output signal is a sample-rate converted representation of the digital input signal with a predetermined target sample rate. The hearing device further comprises a latency controller adapted to estimate the quality of reception of the digital audio signal and to control the processing of the buffered samples in dependence on the estimated quality of reception.
1. A method for operating a hearing device, the method comprising:
receiving samples of a digital audio signal with an input rate;
feeding received samples as a digital input signal to an input buffer;
processing the buffered samples to provide samples of a digital output signal such that the digital output signal is a sample-rate converted representation of the digital input signal with a predetermined target sample rate, said processing comprising upsampling the buffered samples to provide an upsampled signal and downsampling the upsampled signal;
estimating the quality of reception of the digital audio signal by determining an average input buffer level by counting the number of unprocessed samples in the input buffer;
controlling the processing of the buffered samples in dependence on an estimated quality of reception;
increasing a target buffer level when the estimated quality of reception of the digital audio signal decreases;
decreasing the target buffer level when the estimated quality of reception of the digital audio signal increases;
comparing a parameter representative of a difference between the average input buffer level and the target buffer level, or a speed of variation in the difference between the average input buffer level and the target buffer level, to a predetermined threshold; and
controlling a conversion ratio between the input rate and the sample-rate according to one of a first mode and a second mode, which is selected according to a result of the comparison between the parameter and the predetermined threshold, wherein:
in the first mode, the conversion ratio is controlled by performing skip and/or repeat operations in order to minimise the difference between the average input buffer level and the target buffer level,
in the second mode, the conversion ratio is controlled by changing an upsampling factor and/or downsampling factor,
the first mode is selected for controlling the conversion ratio when the parameter is below the predetermined threshold, and
the second mode is selected for controlling the conversion ratio when the parameter exceeds the predetermined threshold thus indicating that the difference between the average input buffer level and the target buffer level is too large or changing too fast to allow minimizing the difference by skip and/or repeat operations.
2. A method according to claim 1 , wherein
said processing comprises computing each sample of the output signal as a scalar product of a subset of the buffered samples and a subset of filter coefficients,
wherein said subsets are selected anew for each computed sample from respectively the input buffer and a set of predetermined coefficients, and
wherein the selection of said subset of the buffered samples is made in dependence on the estimated average or smoothed input-buffer level.
3. A method according to claim 1 , wherein
controlling the processing of the buffered samples comprises proportional-derivative control or proportional-integral-derivative control.
4. A hearing device, comprising:
a receiver,
an input buffer and
a sample processor,
the receiver being adapted to receive samples of a digital audio signal with an input rate and feed received samples as a digital input signal to the input buffer,
the sample processor being adapted to process the buffered samples to provide samples of a digital output signal such that the digital output signal is a sample-rate converted representation of the digital input signal with a predetermined target sample rate, said processing comprising upsampling the buffered samples to provide an upsampled signal and downsampling the upsampled signal, wherein
the hearing device further comprises a latency controller adapted
to estimate the quality of reception of the digital audio signal by counting the number of unprocessed samples in the input buffer and to control the processing of the buffered samples in dependence on the estimated quality of reception,
to increase a target buffer level in dependence on the estimated quality of reception of the digital audio signal decreasing, and
to decrease the target buffer level in dependence on the estimated quality of reception of the digital audio signal increasing,
said hearing device further comprises a ratio controller configured
to compare a parameter representative of a difference between the average input buffer level and the target buffer level, or a speed of variation in the difference between the average input buffer level and the target buffer level, to a predetermined threshold, and
to control a conversion ratio between input rate and the sample-rate according to one of a first mode and a second mode, which is selected according to a result of the comparison between the parameter and the predetermined threshold, wherein:
in the first mode, the conversion ratio is controlled by performing skip and/or repeat operations in order to minimise the difference between the average input buffer level and the target buffer level,
in the second mode, the conversion ratio is controlled by changing an upsampling factor and/or downsampling factor,
the first mode is selected for controlling the conversion ratio when the parameter is below the predetermined threshold, and
the second mode is selected for controlling the conversion ratio when the parameter exceeds the predetermined threshold thus indicating that the difference between the average input buffer level and the target buffer level is too large or changing too fast to allow minimizing the difference by skip and/or repeat operations.
5. A hearing device according to claim 4 , wherein
the sample processor is further adapted to compute each sample of the output signal as a scalar product of a subset of the buffered samples and a subset of filter coefficients,
to select said subsets anew for each computed sample from respectively the input buffer and a set of predetermined coefficients, and
to select said subset of the buffered samples in dependence on the estimated average or smoothed input-buffer level.
6. A hearing device according to claim 5 , wherein
the sample processor is further adapted to shift said subset of the buffered samples in time in dependence on the estimated average or smoothed input-buffer level.
7. The method according to claim 1 , wherein the hearing device being operated is a hearing aid, a listening device, or an active ear-protection device.
8. The hearing device according to claim 4 , comprising at least one of:
a hearing aid;
a listening device; and
an active ear-protection device.