Inquiring minds want to know...
The implementation of the five band graphic equalizer began with reseach on
various types of filters. Searching through textbooks, the internet, and
circuit design books, for schematics of circuits that would be realizable
and functional given the constraints of time, money, and availability of
parts and equipment was at the core of the background work for this
project.
Specifically, the test required the use of active bandpass filters and a
special boost-cut equilizer filter. After obtaining the circuit diagrams
for each filter, the next step required gathering all the circuit
components. All of the components used were readily found in the
laboratory-- resistors, capacitors, 741 op amps, and 100K potentiometers.
Following the circuit diagrams, the equalizer was assembled on two bread
boards. On the other two bread boards the other bandpass filters to be
tested and compared were assembled.
The objective of the test was to synthesize a crop of filters and analyze
their performance. The rigorous methodology of the testing procedure is as
follows:
1. A range of frequencies was selected to analyze each filter. The
frequencies chosen for test points were 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4
kHz, 8kHz, 16kHz.
2. Using a signal generator to create a sinusoid for the input into the
circuit, the output of the filter at each one of these frequencies was run
into an ocilliscope to measure the peak to peak voltage.
3. In addition to testing at the predetermined frequencies, data points
were also taken for frequency values at and around the specific cutoff
frequencies of each one of the filters.
4. The voltage values provided data points for the test frequencies.
Using matlab, the points were plotted. The resulting curve showed the
frequency response of each circuit.
The setup of the Octave Equilizer and the two other filters allowed for
easy modification. By swapping out the existing capacitors in the circuit
for ones of different values, each filter was analyzed at three different
cut off frequencies. To get a more detailed idea of the filter's behavior
at the cutoff frequencies and in this transition area, tests were done at
frequencies just below the cutoff and just above the cutoff.