Guitar Effects Processor Critical Design Review October, 07, 2003

1. Guitar Effects ProcessorCritical Design ReviewOctober, 07, 2003 Groups Members: Adam Bernstein Hosam Ghaith Jasenko Alagic Matthew Iyer Yousef Alyousef

2. System Overview • 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

3. System Block Diagram

4. User Interface • Effect Configuration file • Real-time control software • User program software

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

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

7. User Program Software • 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 • Uses effect configuration file for user-friendly programming

8. State • A State command specifies the intensity of each effect • Examples: • state <id> : <effect_name> <value> <…> • state 0 : distortion 128 octave 64 • state 1 : distortion 192 octave 128 • state 2 : distortion 256 octave 64

9. Sequence • Allows the user to specify a series of states and times • Example: • sequence <id > : <state_id> <time in ms> <…> <end_sequence_tag> <loop_bit> • sequence 0 : 0 0 1 5000 2 10000 % 1

10. Digital Control SystemHC11

11. System Block Diagram

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

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

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

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

16. Port A • 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 • ON0-ON3 bits

17. Port A Connections Effect 0

18. Memory Mapping Scheme

19. Address Decoding SRAM Peripherals EPROM

20. Mixed Signal Interface Communication between HC11 and analog effect circuits

21. System Block Diagram

22. SPI (Serial Peripheral Interface) • The SPI is a typical Master/Slave partnership in which directional communication takes place • 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)

23. Sample SPI Data Transfer

24. SCK MOSI MISO SS1’ SS2’ CNCT’ ON 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

25. Physical SPI Layout

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

27. System Block Diagram

28. Octave Effect Theory • 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.

29. Octave Effect Theory Cont’d • 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 • High-pass filter with cutoff frequency < 80 Hz eliminating the DC-bias of the signal

30. Octave Effect Layout

31. Distortion Effect Theory • 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). • 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.

32. Distortion Effect Layout

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

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

35. Division of Labor

36. Updated Schedule

37. Questions?