Filters and Synthesising signals Flashcards
What is a filter?
A filter is used to extract and amplify important frequencies where undesirable frequencies are also present
What is a (perfect) high-pass filter?
100% of anything larger than a cut-off point will pass through and anything smaller will not
What is a low-pass filter?
100% of anything smaller than the cut off will pass and anything larger will not
How does a real filter differ from the perfect, ideal filter?
-The real filter is imperfect
-It contains a cut- off frequency
-The close you get to the cut off frequency you will start to experience losses
Describe the functions of a real filter
-Cut-off frequency fc
-Characteristic slope
-dB is the gain function of the transfer system where you just take the ratio of the output to the input
What is the significance of -3dB?
It is the point where the output power after the filter is halved
How is -3dB calculated?
0.5= power out
1= power in
What is the slope an indication of?
-How fast the signal attenuates past the cut- off frequency
-If the slope is slow it means it is also allowing lots of things you don’t want to pass
-A fast slope is a more precise filter
How is the slope measured?
As the drop in dB per frequency doubling (octave)
What is a bandpass and bandstop filter?
Bandpass- filters all frequencies to only accept those within the bandwidth
Bandstop- excludes the frequencies within the bandwidth
What is a resonant bandpass filter?
-Filter suppresses all frequencies other than around a centre frequency f0
-The system only responds to a single narrow/ wide frequency band
-Resonances is how many auditory systems work
What is the main application of a filter? Hint: refer to the image
-Filters can be used to clean “dirty data”
-Often data are riddled with low or high frequency noise
-In the left version of the data it looks as though there is no data to analyse, whereas in the right image there is clear data
-The correct usage of a filter could completely transform your data and interpretation of them
What is a lowpass and highpass filter?
-Low pass filter attenuates the high frequency components and preserves the low frequency components
-High pass filter attenuates the low frequency components to preserve the higher frequency components
What is created when two tones of different frequencies are summed together?
A composite signal which contains both frequencies
How do the amplitude, frequency and phase effect synthesis of signals?
- Adding waves of different amplitude= creates the same exact sine wave but just slightly bigger
- Adding waves of different frequency and amplitude= Waves don’t reach certain frequencies at the same time
- Adding waves of different phase= It is possible to lose the signal (antiphase)
What is the sawtooth waveform?
-Has ramps that drop or begin sharply
-To construct it, start with one tone at a specific frequency and add more terms
-As you add more terms you get close and closer to the desired shape
Why does this wave start at 1 even though it has a phase of 0? What is the frequency and phase of this sine wave?
-Because it is based on cosine
-Frequency is 4, phase is 0
