Analogue vs. Digital Signals - ANSWER Auditory perception = analogue
signals stimulating the auditory system
Digital signals = electronic equipment
The main difference = continuity
-analogue signals are continuous and defined at every instant in time
-digital signals are discrete and defined at only certain instances in time
Advantages of digital signals - ANSWER - immune to degradation when
copied
- easier to apply signal processing
- easier to store
Analogue to Digital Conversion and Reconstruction (ADC) - ANSWER
Analog input (sound)
ADC (sampler, discrete-time signal, quantizer)
DSP (digital input to digital output - compression, wind noise filter, adaptive
microphones, etc.)
Reconstruction (DAC to low-pass filter)
Analog output
Sampling - ANSWER The first process in acquiring a digital signal
- measuring and storing the values of an analogue signal
, - Obtained at regular rate as defined by the frequency (fs)
- Each time value associated with each sample can be calculated by knowing
then the period (ps=1/fs)
- Are "held" through the sample period
Sampling Process - ANSWER Produces a spectrum that repeats regularly
- Additional frequency components are introduced into the signal as a result
- The frequency components occur in a regular fashion and are "reflected" about
the y-axis (negative frequencies)
Sampling: Nyquist Theorem - SOLUTION In reconstruction, usually filter out
the replicated spectrum copies
- To retain the signal after filtering and reconstructing it, sampling should be
done at a high enough rate
- The theoretical minimum sampling frequency that will allow the original
signal to be reconstructed has to be at least 2x of the value of the signal's highest
frequency component.
Quantization - ANSWER The process of rounding each of the sampled
analogue values
- Rounding is necessary because digital signals are represented by a limited
number of discrete values known as steps
- Each step has a corresponding binary number
signals stimulating the auditory system
Digital signals = electronic equipment
The main difference = continuity
-analogue signals are continuous and defined at every instant in time
-digital signals are discrete and defined at only certain instances in time
Advantages of digital signals - ANSWER - immune to degradation when
copied
- easier to apply signal processing
- easier to store
Analogue to Digital Conversion and Reconstruction (ADC) - ANSWER
Analog input (sound)
ADC (sampler, discrete-time signal, quantizer)
DSP (digital input to digital output - compression, wind noise filter, adaptive
microphones, etc.)
Reconstruction (DAC to low-pass filter)
Analog output
Sampling - ANSWER The first process in acquiring a digital signal
- measuring and storing the values of an analogue signal
, - Obtained at regular rate as defined by the frequency (fs)
- Each time value associated with each sample can be calculated by knowing
then the period (ps=1/fs)
- Are "held" through the sample period
Sampling Process - ANSWER Produces a spectrum that repeats regularly
- Additional frequency components are introduced into the signal as a result
- The frequency components occur in a regular fashion and are "reflected" about
the y-axis (negative frequencies)
Sampling: Nyquist Theorem - SOLUTION In reconstruction, usually filter out
the replicated spectrum copies
- To retain the signal after filtering and reconstructing it, sampling should be
done at a high enough rate
- The theoretical minimum sampling frequency that will allow the original
signal to be reconstructed has to be at least 2x of the value of the signal's highest
frequency component.
Quantization - ANSWER The process of rounding each of the sampled
analogue values
- Rounding is necessary because digital signals are represented by a limited
number of discrete values known as steps
- Each step has a corresponding binary number
