Frank Vannieuwkerke
Audio Spectrum analyser - FFT using mbed-dsp - driving RGB(W) LED or PC python script.
Dependencies: HSI2RGBW_PWM NVIC_set_all_priorities mbed-dsp mbed FastAnalogIn
Spectrum Analyzer
Code ported from Tony DiCola at AdaFruit FFT: Fun with Fourier Transforms.
Modifications were made to allow the use of the KL25Z on-board RGB LED or an external RGBW power LED.
See items marked with * in the next sections.
Main features
- Uses mbed-dsp library.
- Uses FastAnalogIn to allow a sample rate of 40kHz.
- Display the audio spectrum on a single RGB(W) LED*.
- Display the audio spectrum on your computer using an audio spectrogram tool (python script).
- Change parameters using a terminal connection : Sample rate, min/max db, slowdown*.
Information
Detailed information and download of the python scripts is available here.
KL25Z wiring
Audio inputs
The software samples a single audio channel at 40kHz and applies a Fourier transform to return the frequency spectrum.
Analog input : PTC2.
A DC offset, and possibly some amplification or attenuation, is needed before the signal is fed into the analog inputs.
The opamp choice is not critical, just make sure it supports single supply operation.
Schematic
Currently, only one channel is used when the KL25Z is sampling at 40kHz.
External PWM outputs
| Pin | Color |
| PTD4 | Red |
| PTA12 | Green |
| PTA4 | Blue |
| PTA5 | White |
If you want to use a RGB LED, remove the last pin declaration (PTA5).
The conversion routine automatically switches from HSI/RGBW to HSI/RGB.
To use the external RGBW LED, enable following line in the code:
#define RGBW_ext // Disable this line when you want to use the KL25Z on-board RGB LED.
Commands
Parameters can be altered through the serial port Using a terminal program (eg : TeraTerm).
Communication settings : 38400 baud + local echo.
Each command needs to be terminated with a semicolon.
Use GET <command>; to read a parameter.
Use SET <command> <value>; to set a parameter.
| Command | Description |
| GET MAGNITUDES; | Reads back the FFT magnitudes. Number of magnitudes = PIXEL_COUNT. |
| GET SAMPLES; | Reads back the current samples. Number of samples = PIXEL_COUNT. |
| GET FFT_SIZE; | The size of the FFT. |
| GET SAMPLE_RATE_HZ; | Audio sample rate (Hz). |
| SET SAMPLE_RATE_HZ <value>; | Change the audio sample rate (see also 'Limitations' below). |
| GET LEDS_ENABLED; | LEDs enabled status. |
| SET LEDS_ENABLED <value>; | Control if the LED's should display the spectrum or not. 1 is true, 0 is false. |
| GET SPECTRUM_MIN_DB; | Audio intensity (in decibels) that maps to low LED brightness. |
| SET SPECTRUM_MIN_DB <value>; | Change low sensitivity (0...100dB). |
| GET SPECTRUM_MAX_DB; | Audio intensity (in decibels) that maps to high LED brightness. |
| SET SPECTRUM_MAX_DB <value>; | Change high sensitivity (0...100dB). |
| GET SLOWDOWN; | LED visualisation delay. |
| SET SLOWDOWN <value>; | * Useful to visualize the spectrum using a single RGB(W) LED. Without this command, the color values are shown too fast for the human eye. This allows you to slow down the visualization without interfering in the FFT conversion. Each frequency window is shown a little longer. The number of frequency windows depends on the value of the PIXEL_COUNT variable.[0...999] The larger the value, the longer each frequency window is shown - a good value is 4 when PIXEL_COUNT = 32 (choose a higher SLOWDOWN value when PIXEL_COUNT is lowered). [1000...1000 + PIXEL_COUNT] Selecting a value within this range allows us to lock to a specific frequency window. |
NOTE : PIXEL_COUNT is declared at compile time and determines the number of frequency windows (aka LED colors).
Limitations
The original code was written for a cortex-M4 processor.
For a cortex-M0 processor, following limitations apply:
| SAMPLE_RATE_HZ | FFT_SIZE |
| 1...40000 | max 64 |
Demo Videos
Parameter settings
| SLOWDOWN | 16 (initial value - changed to 1000+ during the video to demonstrate the lock option). |
| SAMPLE_RATE_HZ | 40000 |
| SPECTRUM_MIN_DB | 40.0 |
| SPECTRUM_MAX_DB | 80.0 |
| FFT_SIZE | 64 |
| PIXEL_COUNT | 32 |
Using the on-board RGB LED
SLOWDOWN is set to different values (normal mode and locked mode).
Using an external 10W RGBW LED
SLOWDOWN is set to different values (normal mode and locked mode).
Spectrogram on Computer screen (serial input from KL25Z board
arm_const_structs.h@2:035d551759a5, 2014-03-08 (annotated)
- Committer:
- frankvnk
- Date:
- Sat Mar 08 19:30:20 2014 +0000
- Revision:
- 2:035d551759a5
- Parent:
- 1:736b34e0f484
Replaced deprecated FFT calls with new ones.
Who changed what in which revision?
| User | Revision | Line number | New contents of line |
|---|---|---|---|
| frankvnk | 1:736b34e0f484 | 1 | /* ---------------------------------------------------------------------- |
| frankvnk | 1:736b34e0f484 | 2 | * Copyright (C) 2010-2013 ARM Limited. All rights reserved. |
| frankvnk | 1:736b34e0f484 | 3 | * |
| frankvnk | 1:736b34e0f484 | 4 | * $Date: 17. January 2013 |
| frankvnk | 1:736b34e0f484 | 5 | * $Revision: V1.4.1 |
| frankvnk | 1:736b34e0f484 | 6 | * |
| frankvnk | 1:736b34e0f484 | 7 | * Project: CMSIS DSP Library |
| frankvnk | 1:736b34e0f484 | 8 | * Title: arm_const_structs.h |
| frankvnk | 1:736b34e0f484 | 9 | * |
| frankvnk | 1:736b34e0f484 | 10 | * Description: This file has constant structs that are initialized for |
| frankvnk | 1:736b34e0f484 | 11 | * user convenience. For example, some can be given as |
| frankvnk | 1:736b34e0f484 | 12 | * arguments to the arm_cfft_f32() function. |
| frankvnk | 1:736b34e0f484 | 13 | * |
| frankvnk | 1:736b34e0f484 | 14 | * Target Processor: Cortex-M4/Cortex-M3 |
| frankvnk | 1:736b34e0f484 | 15 | * |
| frankvnk | 1:736b34e0f484 | 16 | * Redistribution and use in source and binary forms, with or without |
| frankvnk | 1:736b34e0f484 | 17 | * modification, are permitted provided that the following conditions |
| frankvnk | 1:736b34e0f484 | 18 | * are met: |
| frankvnk | 1:736b34e0f484 | 19 | * - Redistributions of source code must retain the above copyright |
| frankvnk | 1:736b34e0f484 | 20 | * notice, this list of conditions and the following disclaimer. |
| frankvnk | 1:736b34e0f484 | 21 | * - Redistributions in binary form must reproduce the above copyright |
| frankvnk | 1:736b34e0f484 | 22 | * notice, this list of conditions and the following disclaimer in |
| frankvnk | 1:736b34e0f484 | 23 | * the documentation and/or other materials provided with the |
| frankvnk | 1:736b34e0f484 | 24 | * distribution. |
| frankvnk | 1:736b34e0f484 | 25 | * - Neither the name of ARM LIMITED nor the names of its contributors |
| frankvnk | 1:736b34e0f484 | 26 | * may be used to endorse or promote products derived from this |
| frankvnk | 1:736b34e0f484 | 27 | * software without specific prior written permission. |
| frankvnk | 1:736b34e0f484 | 28 | * |
| frankvnk | 1:736b34e0f484 | 29 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| frankvnk | 1:736b34e0f484 | 30 | * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| frankvnk | 1:736b34e0f484 | 31 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| frankvnk | 1:736b34e0f484 | 32 | * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| frankvnk | 1:736b34e0f484 | 33 | * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| frankvnk | 1:736b34e0f484 | 34 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| frankvnk | 1:736b34e0f484 | 35 | * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| frankvnk | 1:736b34e0f484 | 36 | * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| frankvnk | 1:736b34e0f484 | 37 | * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| frankvnk | 1:736b34e0f484 | 38 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN |
| frankvnk | 1:736b34e0f484 | 39 | * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| frankvnk | 1:736b34e0f484 | 40 | * POSSIBILITY OF SUCH DAMAGE. |
| frankvnk | 1:736b34e0f484 | 41 | * -------------------------------------------------------------------- */ |
| frankvnk | 1:736b34e0f484 | 42 | |
| frankvnk | 1:736b34e0f484 | 43 | #ifndef _ARM_CONST_STRUCTS_H |
| frankvnk | 1:736b34e0f484 | 44 | #define _ARM_CONST_STRUCTS_H |
| frankvnk | 1:736b34e0f484 | 45 | |
| frankvnk | 1:736b34e0f484 | 46 | #include "arm_math.h" |
| frankvnk | 1:736b34e0f484 | 47 | #include "arm_common_tables.h" |
| frankvnk | 1:736b34e0f484 | 48 | |
| frankvnk | 1:736b34e0f484 | 49 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len16 = { |
| frankvnk | 1:736b34e0f484 | 50 | 16, twiddleCoef_16, armBitRevIndexTable16, ARMBITREVINDEXTABLE__16_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 51 | }; |
| frankvnk | 1:736b34e0f484 | 52 | |
| frankvnk | 1:736b34e0f484 | 53 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len32 = { |
| frankvnk | 1:736b34e0f484 | 54 | 32, twiddleCoef_32, armBitRevIndexTable32, ARMBITREVINDEXTABLE__32_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 55 | }; |
| frankvnk | 1:736b34e0f484 | 56 | |
| frankvnk | 1:736b34e0f484 | 57 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len64 = { |
| frankvnk | 1:736b34e0f484 | 58 | 64, twiddleCoef_64, armBitRevIndexTable64, ARMBITREVINDEXTABLE__64_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 59 | }; |
| frankvnk | 1:736b34e0f484 | 60 | |
| frankvnk | 1:736b34e0f484 | 61 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len128 = { |
| frankvnk | 1:736b34e0f484 | 62 | 128, twiddleCoef_128, armBitRevIndexTable128, ARMBITREVINDEXTABLE_128_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 63 | }; |
| frankvnk | 1:736b34e0f484 | 64 | |
| frankvnk | 1:736b34e0f484 | 65 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len256 = { |
| frankvnk | 1:736b34e0f484 | 66 | 256, twiddleCoef_256, armBitRevIndexTable256, ARMBITREVINDEXTABLE_256_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 67 | }; |
| frankvnk | 1:736b34e0f484 | 68 | |
| frankvnk | 1:736b34e0f484 | 69 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len512 = { |
| frankvnk | 1:736b34e0f484 | 70 | 512, twiddleCoef_512, armBitRevIndexTable512, ARMBITREVINDEXTABLE_512_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 71 | }; |
| frankvnk | 1:736b34e0f484 | 72 | |
| frankvnk | 1:736b34e0f484 | 73 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len1024 = { |
| frankvnk | 1:736b34e0f484 | 74 | 1024, twiddleCoef_1024, armBitRevIndexTable1024, ARMBITREVINDEXTABLE1024_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 75 | }; |
| frankvnk | 1:736b34e0f484 | 76 | |
| frankvnk | 1:736b34e0f484 | 77 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len2048 = { |
| frankvnk | 1:736b34e0f484 | 78 | 2048, twiddleCoef_2048, armBitRevIndexTable2048, ARMBITREVINDEXTABLE2048_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 79 | }; |
| frankvnk | 1:736b34e0f484 | 80 | |
| frankvnk | 1:736b34e0f484 | 81 | const arm_cfft_instance_f32 arm_cfft_sR_f32_len4096 = { |
| frankvnk | 1:736b34e0f484 | 82 | 4096, twiddleCoef_4096, armBitRevIndexTable4096, ARMBITREVINDEXTABLE4096_TABLE_LENGTH |
| frankvnk | 1:736b34e0f484 | 83 | }; |
| frankvnk | 1:736b34e0f484 | 84 | |
| frankvnk | 1:736b34e0f484 | 85 | #endif |
| frankvnk | 1:736b34e0f484 | 86 |