Auto Harmonizer - University of Florida · 2012. 8. 29. · increased noise, small dynamic range...
Transcript of Auto Harmonizer - University of Florida · 2012. 8. 29. · increased noise, small dynamic range...
Auto Harmonizer
EEL 4924 Electrical Engineering Design (Senior Design)
Final Design Report
26 April 2012
Team Name: Slubberdegullions
Team Members: Josh Elliott and Henry Hatton, Jr.
Project Abstract:
Our project consists of creating an Auto Harmonizer which will capture an audio
signal and generate a harmonized output in real time. This project will rely extensively on
digital signal processing to accomplish the harmonization, but will also utilize analog
circuitry to allow for the inclusion of adjustable equalization. The device will be able to take
an analog input from an XLR port or a ¼ inch audio jack, pre-amplify the input signal,
condition it for the DSC, and mix the original signal and the harmonized signal before
sending them to the equalizer. Additionally, users will be able to customize the response of
the device through the use of knobs which will adjust the equalization of the output signal.
The two most important technical components of this project are the programming of the
DSC and the design of the analog equalization circuitry.
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Table of Contents Introduction..………………………………………………………………..............................3
Objectives………………………………………………………………...................................3
Design Aspect Digital / DSP………………………………………………..............................4
Design Aspect Analog…………………………………………………………….……….......6
Analog Equalization Technology……………...........................................................................9
Cost Estimate…………………..…………...............................................................................9
Division of Labor…………..…………….................................................................................9
List of Tables 1. Center Frequency Bands…………………………………………………....................6
List of Figures 1. System Flowchart….....…………………………………………………......................3
2. Software Flowchart ………….....………......................................................................5
3. Initial Band-Pass Filter Configuration…..…….............................................................6
4. Revised circuit Configuration utilizing Notch filters…....…………...……………….7
5. Balanced to Line Mic Preamp………………………………...……………………….8
6. DC Offset and 1k Hz LPF……………………………………………………………..8
7. Mixer Amplifier……………………………………………………………………….8
8. Gantt Chart…….………….....……….........................................................................10
9. XLR Balanced to Line Mic Preamp…………….……………………………………10
10. Housing……………...……………………………………………………………….11
11. 5 Band Equalizer………………………………………………………………..……11
12. DSP……………...……………………………………………………………………12
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Introduction
The heart of this project lies in the development of a system that will allow the user to
harmonize an input signal with at least one harmonized output. Furthermore, the user will
need to be able to modify the quality of the out through an adjustable, analog equalization
circuit. Figure 1 below shows the System Flowchart.
INPUT Balanced XLR
or¼“ Jack
DSP
Mixing Amplifier
OUTPUT¼ “ Jack
Balanced to Line Level
DC OffsetParametric
Equalization1 KHz LPF
Figure 1 System Flowchart
Project Objectives – Digital / DSP
Real-time harmonization of an input signal with a sample from memory.
The input is recorded for a short period of time; data capture occurs at the behest of an
external trigger. Data output also happens in response to a hardware trigger.
The input signal can be any periodic audio signal.
FFTs are used to create proper harmonies.
Project Objectives – Analog
Proving a balanced XLR to line level or ¼” input jack.
Pre-amplifying the microphone input signal.
Providing a DC offset for an optimal input to the DSP
Providing 5 bands of equalization to include the following center frequency channels
shown in Table 1.
Utilizing active low-pass and notch filters.
Minimize noise in the system.
Reduce RF susceptibility.
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Design Aspect – Digital / DSP
Overview
This portion of the project relies extensively on the use of software algorithms
implemented on a TI DSC to produce the required digital signal processing necessary to
accomplish harmonization. Some key factors that guided the design process are as follows:
Utilization of TMS320F28335 DSC (Used in EEL4744)
Chosen because of familiarity and processing capabilities
Not a heavy hitting DSP, but its use greatly simplified potential design problems
that would have been salient with less powerful microprocessors
Immediate availability of dev-board for early testing and development
Extensive amount of resources and support readily available on campus
Real-time Harmonization
Required much software optimization, but proved to be possible
Delayed output of harmony is very small
Assumption of Periodic Input
Made discerning the fundamental frequency more attainable
A signal with a primary frequency component caused frequency domain operations
to be simpler
Fast Fourier Transforms
Difficult algorithm to get properly functioning on a small DSC
Utilizing existing TI libraries made the process easier
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Software Flowchart
The flowchart in Figure 2 below describes the basic structure of the algorithm that is
used to accomplish the harmonization of the signal. The software flow depicted below
occurs at every instance in which an external trigger is detected.
Receive Audio from ADC
Take FFT
Prepare Audio for FFT
(windowing, etc)
Find Fundamental Frequencies
Quadratic Interpolation to
Improve FrequencyResolution
Compare Frequency with LUT to find “in
tune” note
Output Desired Harmony
Figure 2 Software Flowchart
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Design Aspect – Analog
Provide a multi-band active parametric equalizer to fine tune the harmonized output
signal. Active filters are favored for the low cost, light weight, small size and gain
availability. Utilizing 2nd
order filters consisting of 2 capacitors and 2 resistors. The center
frequency (fₒ) bands are shown below in Table 1.
Table 1
Center Frequency Bands
Band fₒ (Hz)
1 32
2 125
3 500
4 2,000
5 16,000
We experimented with various circuit configurations for the active band-pass filters.
The initial circuit configuration for one of the band-pass filters is shown below in Figure 3.
Figure 3 Initial Band-Pass Filter Circuit Configuration
Design Challenges
The difficulty with the initial circuit configuration was too much gain for the audio
operational amplifiers. After adjusting the filters to unity gain a cleaner, less distorted audio
signal passed through the filter stages. Additional problems with the analog circuitry were
with the PCB. Narrow trace separation width increased noise in the system.
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Revised Notch Filter Design
Figure 4 below shows the revised equalization circuitry
Figure 4 Revised circuit Configuration utilizing Notch filters
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Figure 5 shows the design for the Balanced XLR input to line level input microphone
preamplifier.
Figure 5 Balanced to Line Mic Preamp
Figure 6 shows the design for the DC offset to provide the DSP input with a level of
approximately 1.5 Volts and a 1 kHz LPF to make the signal processing easier.
Figure 6 DC Offset and 1 kHz LPF
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Figure 7 shows the mixer amplifier design.
Figure 7 Mixer Amplifier
Analog Equalization Technology
Equalization filter circuitry is used in applications such as program enhancement,
sound reinforcement, telecommunications and data acquisition. There are many different
types of equalizers. A passive equalizer consists of inductors, capacitors and resistors and
does not require power to operate. The advantages for the passive equalizer are low noise
performance, good reliability, low RFI interference susceptibility and high dynamic range.
The disadvantages for passive equalizer are large size, weight, cost and the need for
shielding. The active equalizer features operational amplifiers and various other components
and require power to operate. The advantages for active equalizers are small size, light
weight, low cost and gain availability. The disadvantages for the active equalizer are
increased noise, small dynamic range and RFI susceptibility.
Division of Labor
Josh Elliott
Interfacing of DSC with peripherals
DSP software algorithms for DSC
PCB for DSC and digital components
Henry Hatton, Jr.
Design of the Balanced to Line Mic Preamplifier
Design of the DC Offset circuitry and 1 kHz LPF
Design of the equalization circuitry
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Design of the 2 PCB boards for the analog circuitry
Figure 8 Gantt chart
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Figure 9 – XLR Balanced to Line Mic Preamp
Figure 10 – Housing
Figure 11 – 5 Band Equalizer
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Figure 12 – DSP