# IIR Filter Example
(See the README.md file in the upper level 'examples' directory for more information about examples.)
This example demonstrates how to use IIR filters functionality from esp-dsp library. Example does the following steps:
1. Initialize the library
2. Initialize input signal
3. Show LPF filter with Q factor 1
* Calculate iir filter coefficients
* Filter the input test signal (delta function)
* Shows impulse response on the plot
* Shows frequency response on the plot
* Calculate execution performance
4. The same for LPF filter with Q factor 10
## How to use example
### Hardware required
This example does not require any special hardware, and can be run on any common development board.
### Configure the project
Under Component Config ---> DSP Library ---> DSP Optimization, it's possible to choose either the optimized or ANSI implementation, to compare them.
### Build and flash
Build the project and flash it to the board, then run monitor tool to view serial output (replace PORT with serial port name):
```
idf.py -p PORT flash monitor
```
(To exit the serial monitor, type ``Ctrl-]``.)
See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
## Example output
Here is an typical example console output.
```
I (58) main: Start Example.
I (58) main: Impulse response of IIR filter with F=0.100000, qFactor=1.000000
I (68) view: Data min[8] = -0.060052, Data max[2] = 0.333517
________________________________________________________________
0 |
1 |
2 - |
3- - |
4 -------------------------------------------------------------|
5 |
6 |
7 |
8 |
9 |
0123456789012345678901234567890123456789012345678901234567890123
I (138) view: Plot: Length=128, min=-1.000000, max=1.000000
I (148) view: Data min[511] = -149.983795, Data max[0] = 0.000000
________________________________________________________________
0 |
1 |
2----------------- |
3 ---------- |
4 ------------- |
5 ---------- |
6 ------- |
7 --- |
8 -- |
9 --|
0123456789012345678901234567890123456789012345678901234567890123
I (228) view: Plot: Length=512, min=-100.000000, max=0.000000
I (228) main: IIR for 1024 samples take 20276 cycles
I (238) main: Impulse response of IIR filter with F=0.100000, qFactor=10.000000
I (248) view: Data min[7] = -0.453739, Data max[2] = 0.526114
________________________________________________________________
0 |
1 |
2 - - |
3- - - - --- --- - - |
4- - - - - ---- -------------------------------------|
5 -- -- -- -- |
6 |
7 |
8 |
9 |
0123456789012345678901234567890123456789012345678901234567890123
I (318) view: Plot: Length=128, min=-1.000000, max=1.000000
I (328) view: Data min[511] = -149.480377, Data max[0] = 0.000000
________________________________________________________________
0 -- |
1 -- - |
2---------- ----- |
3 -------- |
4 ------------ |
5 ---------- |
6 ------- |
7 --- |
8 -- |
9 --|
0123456789012345678901234567890123456789012345678901234567890123
I (408) view: Plot: Length=512, min=-100.000000, max=0.000000
I (408) main: IIR for 1024 samples take 17456 cycles
I (418) main: End Example.
```
To create a project from this example, run:
idf.py create-project-from-example "espressif/esp-dsp=1.4.11:iir"