Guitar Effects Processor Critical Design Review October, 07, 2003 Groups Members: Adam Bernstein Hosam Ghaith Jasenko Alagic Matthew Iyer Yousef Alyousef

System Overview Guitar effects generator Guitar effects generator –Takes input from standard audio source and produces output to standard amplifiers in real- time output –Employs a modular design of effects including “Distortion” and “Octave” circuits –Is programmed by musician though user friendly interface –Produces good audio quality

System Block Diagram

User Interface Effect Configuration file Effect Configuration file Real-time control software Real-time control software User program software User program software

Effect Configuration File Specify port-to-effect mapping Specify port-to-effect mapping Enables software to be user friendly Enables software to be user friendly Example: Example: –port 0 : Distortion –port 1 : Octave

Real-time Control Software Reads effect configuration file and generates a GUI Reads effect configuration file and generates a GUI Demo! Demo!

User Program Software A user program consists of two simple commands: A user program consists of two simple commands: –State –Sequence of State commands in time Software interprets an ASCII file containing commands and sends it to the HC11 to be stored in SRAM Software interprets an ASCII file containing commands and sends it to the HC11 to be stored in SRAM Uses effect configuration file for user- friendly programming Uses effect configuration file for user- friendly programming

State A State command specifies the intensity of each effect A State command specifies the intensity of each effect Examples: Examples: –state : –state : –state 0 : distortion 128 octave 64 –state 1 : distortion 192 octave 128 –state 2 : distortion 256 octave 64

Sequence Allows the user to specify a series of states and times Allows the user to specify a series of states and times Example: Example: –sequence : –sequence : –sequence 0 : % 1

Digital Control System HC11

System Block Diagram

EPROM Contents Code to Initialize the system Code to Initialize the system Interrupt driven serial communication with PC Interrupt driven serial communication with PC Code to write to the SPI interface to adjust effects Code to write to the SPI interface to adjust effects Code to interpret user programs Code to interpret user programs

SRAM Save the current system state Save the current system state –Store connected effect circuits –Store effects variables Store user programs (loaded from user interface) Store user programs (loaded from user interface)

Peripherals Support for up to 4 effect circuits Support for up to 4 effect circuits Each effect circuit can have 2 digitally controlled devices Each effect circuit can have 2 digitally controlled devices

Communication with Peripherals Serial Peripheral Interface (SPI) to communicate with effect circuits Serial Peripheral Interface (SPI) to communicate with effect circuits RS-232 interface to communicate with PC (user interface) RS-232 interface to communicate with PC (user interface) I/O port (Port A) I/O port (Port A) –Turn effects on/off –Determine which effects are connected

Port A 4 out of the 8 pins will be used as parallel inputs 4 out of the 8 pins will be used as parallel inputs –Used to detect which effects are connected. –CNCT0’-CNCT3’ bits (active low) The rest are used as outputs to turn effects on and off The rest are used as outputs to turn effects on and off –ON0-ON3 bits

Port A Connections Effect 0

Memory Mapping Scheme

Address Decoding SRAM Peripherals EPROM

Mixed Signal Interface Communication between HC11 and analog effect circuits

System Block Diagram

SPI (Serial Peripheral Interface) The SPI is a typical Master/Slave partnership in which directional communication takes place The SPI is a typical Master/Slave partnership in which directional communication takes place There are four channels that make up this interface There are four channels that make up this interface –SCLK (Serial Clock) –MOSI (Master Out Slave In) »One way communication channel from the master to the slave(s) –MISO (Master In Slave Out ) »Opposite of MOSI –SS (Slave Select) »The request line controlled by the master to initiate communication with the slave(s)

Sample SPI Data Transfer

Connection between Effect and HC11 SCK: Serial Clock MOSI: Master Out Slave In MISO: Master In Slave Out SS’: Slave Select bits (Active Low) Multiplexed CNCT’: Device connected bit (Active Low) ON: Turns device on MOSIMISOSS1’SCKSS2’CNCT’ON

Physical SPI Layout

Xicor X9250 Xicor X9250 Digitally Controlled Potentiometer Digitally Controlled Potentiometer Turns on/off a series of ~1000 gates moving a “Wiper Arm” up and down the potentiometer altering the effective resistance Turns on/off a series of ~1000 gates moving a “Wiper Arm” up and down the potentiometer altering the effective resistance

System Block Diagram

Octave Effect Theory The octave effect doubles the frequency of the input signal then superimposes the new signal onto the original sound The octave effect doubles the frequency of the input signal then superimposes the new signal onto the original sound The user controls how much the original signal is to be mixed back in with its octave. The user controls how much the original signal is to be mixed back in with its octave.

Octave Effect Theory Cont’d The input signal is first passed through a full wave rectifier creating the following signal The input signal is first passed through a full wave rectifier creating the following signal Lowpass filter to “smooth out” sharp edges, effectively creating DC- biased sinusoid Lowpass filter to “smooth out” sharp edges, effectively creating DC- biased sinusoid High-pass filter with cutoff frequency < 80 Hz eliminating the DC-bias of the signal High-pass filter with cutoff frequency < 80 Hz eliminating the DC-bias of the signal

Octave Effect Layout

Distortion Effect Theory Signal is clipped from both the top and bottom, effectively adding higher frequency harmonics. Signal is clipped from both the top and bottom, effectively adding higher frequency harmonics. The two voltage levels at which the signal is clipped are fixed. To increase distortion, the input signal is amplified, leading to more distortion but also to higher volume (increased RMS value). The two voltage levels at which the signal is clipped are fixed. To increase distortion, the input signal is amplified, leading to more distortion but also to higher volume (increased RMS value). To keep volume fixed: a gain stage must be cascaded decreasing the amplitude of the output signal at the same rate that the distortion is increased. To keep volume fixed: a gain stage must be cascaded decreasing the amplitude of the output signal at the same rate that the distortion is increased.

Distortion Effect Layout

Milestone I Goals Design and fully implement analog effect circuits using knob potentiometers as effect intensity controllers Design and fully implement analog effect circuits using knob potentiometers as effect intensity controllers Implement real-time computer GUI interface Implement real-time computer GUI interface Be able to read/write to SRAM with microprocessor Be able to read/write to SRAM with microprocessor

Milestone II Be able to communicate to PC via RS-232 Be able to communicate to PC via RS-232 Write software to parse an effects program file Write software to parse an effects program file Program digitally controlled components through SPI Program digitally controlled components through SPI Replace knob analog potentiometers with digitally controlled components Replace knob analog potentiometers with digitally controlled components

Division of Labor Tasks: Done by: Design and Implementation of Distortion Circuit Adam, Jasenko and Hosam Design and Implementation of Octave Circuit Adam, Jasenko and Hosam Mixed-Signal Interface Adam, Jasenko, Yousef, Hosam Microprocessor/Software Matthew, Yousef Systems Integration Everybody Testing and Quality Assurance Everybody

Updated Schedule

Questions?