DSP 1 MAIN EXAMINATION SET QUESTIONS AND
ANSWERS GRADED A+
✔✔A hearing aid can only amplify sounds up to about - ✔✔40% to 45% of the sampling
rate (theoretical maximum 50%)
✔✔If sampling rate is unnecessarily high - ✔✔complexity of the processing will be
limited
✔✔Hearing aids usually have sampling rates ranging from - ✔✔16,000 to 32,000 Hz
✔✔The digital representation of sound is determined by - ✔✔sampling rate
✔✔Bits - ✔✔binary digits (0,1)
✔✔Increasing the number of bits increases - ✔✔the number of values
✔✔each additional bit will - ✔✔double the number of possible values and in doing so
provides a 6 dB increase in dynamic range
Example: a 16 bit system will have a theoretical dynamic range(DR) of 16x6dB = 96dB
DR, 12 bit system = 12x6dB = 72dB DR
But in real life, it's 3-10% less than theoretical limits
✔✔Typically modern aids use bit values of - ✔✔12 -24 bits
✔✔Too few bits results in a limited - ✔✔DR and limited input ceiling
✔✔(PAST) to avoid digital clipping with high input levels, sounds in the environment
above 83 dB - 88 dB.... - ✔✔were not allowed into the hearing aid
✔✔To avoid this limitation, we now use - ✔✔higher bit #
✔✔The greater number of bits, the greater... - ✔✔number of analog voltage levels
represented
✔✔The greater number of bits, the less.... - ✔✔less quantization noise
✔✔more bits require.... - ✔✔more power and result in more battery drain
, WE NEED TO BALANCE FOR ACCURATE REPRESENTATION (depends on desired
DR)
✔✔Current consumption and hence battery life and battery size, depends on -
✔✔instruction rate, the voltage of the integrated circuits, and the technology used to
make the integrated circuit
None of this is under the control of the clinician
✔✔Processing Delay definition - ✔✔The delay from input to output of the hearing aid
✔✔Longer delay degrades - ✔✔signal quality, (for the hearing aid wear's own voice)
✔✔longer delays facilitate more - ✔✔sophisticated signal processing that allows the
hearing aid to react smoothly to changes in the signal
✔✔Total delay definition - ✔✔the amount of time sound is delayed by the hearing aid
✔✔Group delay definition - ✔✔The number of frequency ranges used for processing
and how those frequency ranges are broken up that effect processing time.
✔✔Today the delay we measure is between - ✔✔2 - 8ms
✔✔Delays less than 9-10ms are generally considered - ✔✔too small to be problematic.
✔✔Delays in the range of 10-15ms have been shown - ✔✔to be objectionable to
listeners with normal hearing but those with hearing loss have been shown to tolerate
longer delays of 14-30ms
✔✔Patients don't have the same type of hearing loss at all frequencies, so it is
necessary to - ✔✔apply different processing at different frequency regions.
✔✔Fast Fourier Transform definition - ✔✔transform the time domain representation into
a frequency domain representation
✔✔Advantages of working in the frequency domain - ✔✔-More computationally efficient
(the HA can calculate more algorithms with the same total processing power)
-Provides blocks of FQ specific data that can be sequentially compared (this is useful
for HA features such as wind noise detection, feedback suppression etc)
ANSWERS GRADED A+
✔✔A hearing aid can only amplify sounds up to about - ✔✔40% to 45% of the sampling
rate (theoretical maximum 50%)
✔✔If sampling rate is unnecessarily high - ✔✔complexity of the processing will be
limited
✔✔Hearing aids usually have sampling rates ranging from - ✔✔16,000 to 32,000 Hz
✔✔The digital representation of sound is determined by - ✔✔sampling rate
✔✔Bits - ✔✔binary digits (0,1)
✔✔Increasing the number of bits increases - ✔✔the number of values
✔✔each additional bit will - ✔✔double the number of possible values and in doing so
provides a 6 dB increase in dynamic range
Example: a 16 bit system will have a theoretical dynamic range(DR) of 16x6dB = 96dB
DR, 12 bit system = 12x6dB = 72dB DR
But in real life, it's 3-10% less than theoretical limits
✔✔Typically modern aids use bit values of - ✔✔12 -24 bits
✔✔Too few bits results in a limited - ✔✔DR and limited input ceiling
✔✔(PAST) to avoid digital clipping with high input levels, sounds in the environment
above 83 dB - 88 dB.... - ✔✔were not allowed into the hearing aid
✔✔To avoid this limitation, we now use - ✔✔higher bit #
✔✔The greater number of bits, the greater... - ✔✔number of analog voltage levels
represented
✔✔The greater number of bits, the less.... - ✔✔less quantization noise
✔✔more bits require.... - ✔✔more power and result in more battery drain
, WE NEED TO BALANCE FOR ACCURATE REPRESENTATION (depends on desired
DR)
✔✔Current consumption and hence battery life and battery size, depends on -
✔✔instruction rate, the voltage of the integrated circuits, and the technology used to
make the integrated circuit
None of this is under the control of the clinician
✔✔Processing Delay definition - ✔✔The delay from input to output of the hearing aid
✔✔Longer delay degrades - ✔✔signal quality, (for the hearing aid wear's own voice)
✔✔longer delays facilitate more - ✔✔sophisticated signal processing that allows the
hearing aid to react smoothly to changes in the signal
✔✔Total delay definition - ✔✔the amount of time sound is delayed by the hearing aid
✔✔Group delay definition - ✔✔The number of frequency ranges used for processing
and how those frequency ranges are broken up that effect processing time.
✔✔Today the delay we measure is between - ✔✔2 - 8ms
✔✔Delays less than 9-10ms are generally considered - ✔✔too small to be problematic.
✔✔Delays in the range of 10-15ms have been shown - ✔✔to be objectionable to
listeners with normal hearing but those with hearing loss have been shown to tolerate
longer delays of 14-30ms
✔✔Patients don't have the same type of hearing loss at all frequencies, so it is
necessary to - ✔✔apply different processing at different frequency regions.
✔✔Fast Fourier Transform definition - ✔✔transform the time domain representation into
a frequency domain representation
✔✔Advantages of working in the frequency domain - ✔✔-More computationally efficient
(the HA can calculate more algorithms with the same total processing power)
-Provides blocks of FQ specific data that can be sequentially compared (this is useful
for HA features such as wind noise detection, feedback suppression etc)
