Digital Equalizer Functional description
Description: The system will be a digital equalizer. The user will be able to change the volume control and the relative weights of frequency bands. Both of these characteristics of the input sound will be controlled by a rotary switch. The user can also display either a oscilloscope or spectrum analyzer display to analyze the input waveform. The user can also select between percent increments or decibel increments in gain, as well as putting the equalizer in pass through mode. Finally, the user can select a preset programmed in memory.
Input:
The input of the system
will be sound waveform, from either a microphone or music player, going through
a stereo jack. The user will input commands through the rotary switches to
increase the gain of a specific band of frequency. There will be frequency
selecting buttons to determine which frequency band will have its gain changed.
Turning a knob will increase or decrease the weight of a frequency band or the
volume. The user can also alternate control between the left channel and right
channel if the input is stereo. The selection of menu items will also be done
via push buttons.
User Interface
On power up, the digital
equalizer will start in the “on” mode. Once activated, the equalizer’s volume
control and frequency band controls will take effect, manipulating the input
signal as the user wishes:
|
Rotary switches actions |
Valid in Which
menus |
Description of
Turn Action |
|
Volume control |
All menus, when the volume band is selected |
The user can vary the volume of the output from 0% to 100%, or –20 dB to +20dB (relative to some set output level). The volume level will increase or decrease in increments of 5% or 1 dB. Clockwise increases, while Counterclockwise decreases. |
|
Frequency band control |
All menus, when one of the frequency bands is selected |
The user can vary the weight of the frequency band from 0% to 100%, or –20 dB to +20dB (relative to some set weight). The frequency band weight will increase or decrease in increments of 5% or 1 dB. Clockwise increases, while Counterclockwise decreases. |
|
Key Switch |
|
Description of Key Action |
|
<Up> |
All menus |
Move the cursor up to the previous menu, if not already at the top menu item. If the cursor is at the top of the menu, then the cursor will not be moved. |
|
<Down> |
All menus |
Move the cursor down to the next menu, if not already at the bottom menu item. If the cursor is at the bottom of the menu, then the cursor will not be moved. |
|
<Select> |
|
Change the settings of the current sub-menu |
|
<Left> |
All menus, except the Presets menu. |
Selects a band (including volume) to the left of the one currently selected. It will not select anything to the left of the volume band. In the presets menu, this option will select one of the presets. |
|
<Right> |
All menus, except the Presets menu. |
Selects a band (including volume) to the right of the one currently selected. It will not select anything to the right of the volume band. In the presets menu, this option will select one of the presets. |
|
Menu |
Options |
Description |
|
Channel |
Left, Right |
In the menu, the select
button toggles the equalizer control between the left channel and right
channel. When the equalizer is controlling the left channel, the rotary
control and the channel selecting controls will affect the volume and
frequency weights of the left channel. When the equalizer is controlling the
right channel, the rotary control and channel selecting controls will control
the volume and frequency weights of the right channel. |
|
Equalizer |
On, Off |
In the menu, the select
button toggles the equalizer between the on/off modes. When the equalizer is
on, the volume control and frequency band controls will take effect. In the
off mode, the system simply acts as a pass through system. |
|
Analyzer |
Spectrum analyzer,
Oscilloscope |
In the menu, the select
button toggles the analyzer between spectrum mode and scope mode. In the
spectrum analyzer mode, the display will display the frequency response at
various frequencies. In the scope analyzer mode, the display will show the
output waveform. |
|
Increments select |
Percent, Decibel |
In the menu, the select
button toggles the increments between percent increments and decibel
increments. The percent increments change the gain for everything in
increments of 5%. The decibel increments change the gain for everything in
increments of 1 dB. |
|
Presets |
Default, High pass, Low
pass |
In the menu, the menu
button now selects the default preset (where every frequency badn is passed
evenly). The left button selects the high pass preset (high frequencies are
passed). The right button selects the low pass preset (low frequencies are
passed). |
|
Frequency bands |
Set at 60, 170, 310, 600,
1k, 3k, 6k, 12k, >12k (all in Hz) |
The frequency band for
the selected channel is selected by the left and right push buttons.Turning
the rotary knob for t frequency band will change value for that band on the
display, and increment/decrement the weighting of the band by the option
chosen in the increments menu. |
|
Volume Control |
- |
Same controls as the
frequency bands |
For additional details, see User Manual.
Additional Software Functional specifications:
As described by the top proposal page, the system convolutions and frequency responses will be done by:
, 
respectively. Given the volume and frequency controls, software will display the appropriate value for controls on the displays. Given the frequency responses (i.e. the H[z] above), software will display appropriate length bars on the display.
The scope mode will display the waveform directly.
Output:
The display for the system will be a Federal Express Surplus graphical LCD (128 x 480 pixels). The screen will display:
- The menu system described above.
- The current status of the volume and frequency controls (the percentage weight will be displayed) for both the left and right channel.
- The response in each frequency band (in spectrum analyzer mode) or the waveform (in scope mode) will be displayed. The spectrum analyzer will be in bar chart form for both the left and right channel. This will be refreshed as fast as the LCD refresh rate, or as fast as the samples come in. The scope analyzer will be in line graph form, and will be updated just as fast.
Return values: None (only power down for the stand alone system)
Arguments: None
Error Handling:
If there is a power failure
the system will be reset to the start state, where it will be a pass-through
system.
Algorithms:
- DFT (discrete Fourier Transform) algorithm (Appendix A)
- Signal convolution algorithm (Appendix B)
Data structure:
- Every control will have a percentage associated with it, and displayed on the screen.
- Every line on the bar chart of the frequency response will represent a certain percentage weight on the display.
- The samples will be in 24-bit form.
Limitations:
- RAM size (4k usable program memory, 2k of X and Y usable processing memory)
- ROM size (4k x 24 bits of program memory space on DSP = 12k x 8 bits on ROM)
- The sampling will be conducted at 56kHz. If this is the Nyquist frequency, then maximum frequency allowed in the system is 28kHz. The anti-aliasing filter in the A/D should take care of this.
- sampling resolution of 24 bits
- resolution of display: 1 line on the frequency response chart represents some percentage.
- The plot pixel time of the LCD hinders the rate at which the display can be plotted. Because the read and write times to the LCD are extremely long, their cycles sometimes overruns the receive and transmit interrupts. This is dealt with in software.