5 - Digital Technology Flashcards
What are three types of HAs?
1) analog
2) programmable (digitally controlled analog)
3) digital
What are 3 components of analog HAs?
1) The electrical voltage is analogous to the acoustic signal
2) Analog HA are now obsolete
3) Processing was 1:1 up to the output limit of the hearing aid
What are 2 components of programmable HAs?
1) Programming is performed through digital technology but signal processing remains analog
2) Also obsolete
What are 2 components of digital HAs?
1) Digital processing of signals
2) Classified as entry, intermediate, and advanced levels depending on features available.
How does processing happen in analog HAs?
Mic—amplifier—receiver
How does processing happen in digital HAs?
Mic—preamp—LP filter—digital conversion—digital signal processing—analog conversion—LP filter—receiver
How does a HA process sound?
- Sound: condensations and rarefactions of air (particles moving back and forth over time)
- HAs break up this continuous information, break it down, store it, and put it back together
- HAs are recording this, and reproduce after the signal has been manipulated
What are the 4 steps of how digital HAs process sound?
1) Mic picks up signal and converts it into electrical energy
2) Analog to Digital Conversion (ADC or A/D)
3) Digitized numerical codes are assigned binary digits (bits) or “0” and “1”.
- Signal processing occurs through manipulation of these digits
4) Digital to Analog Conversion (DAC or D/A)
How can a HA represent sound well?
- There has to be enough samples to accurately represent the information
- Specifically, we must consider the NYQUIST theorem.
- We need at least double the sampling points as the highest frequency we want to represent.
- The Nyquist FREQUENCY is half the sampling rate.
What is the aliasing error?
When the input frequency is greater than the Nyquist frequency, a “new” sine wave, not present in the original signal, is created
- aliasing signal
- distortion
What is a visual example of the aliasing error?
Visual example: car wheels that appear to turn backwards in movies
- Camera samples the movement at specific times
- The wheel turns faster than the sampling frequency
How are HAs understanding sound?
HAs understand sounds as discrete points of information
What if there aren’t enough sound points to represent the sine wave?
- If not enough points to represent the sine wave, it will fill in the blanks
- If we don’t have a good signal understanding on the input, the output cannot be beneficial and accurate
Analog to digital conversion - how do you avoid aliasing in HAs?
- Problem of aliasing if input signal contains frequencies above the Nyquist frequency.
- Low-pass filter (anti-aliasing filter) rejects the frequencies higher than the Nyquist prior to A/D conversion.
Where does the anti-aliasing filter happen in digital HAs?
Anti-aliasing happens before the digital conversion of the signal