Continuous Frequency Synthesizer

1. Continuous Frequency Synthesizer Continuous Frequency Synthesizer Presented by: Andrew Latham Daniel Pfeiffer Omar Khan Presented by: Andrew Latham Daniel Pfeiffer Omar Khan

2. What Is A Theremin?

3. Theremin in action

4. History • First electronic instrument, circa 1921 • 1929 – RCA buys rights to manufacture • 1954 – Robert Moog (of synthesizer fame) starts production • Used by such diverse bands as The Beach Boys, Led Zeppelin, and Nine Inch Nails.

5. Theremin in concert

6. General Overview • Analog Theremin • Perform synthesis using DSP and FPAA (Field Programmable Analog Array) • User-specified set of synthesis techniques and effects

7. Objectives • Incorporate multiple facets of ECE: 1. Analog circuitry 2. Digital Signal Processing 3. Electro-magnetics • Create a working analog and digital Theremin. • Unique • Fun!

8. Original Design • Single Antenna • Volume Dial • Synthesis using DSP • Additional effects by FPAA • FPAA output to amplifier

9. Original Design • Types of Synthesis: 1. Additive • Harmonics 2. Subtractive • Use analog filtering • Sawtooth • Triangle • Pulse • Additional Effects: •Tremolo • Reverb • Vibrato

10. Final Design • Single Antenna • Synthesis using DSP • Add’l filtering by FPAA • Volume Control and DC, Highpass filters • Output to Amplifier

11. Theremin Circuit

12. Power Circuit

13. Oscillator 1

14. Oscillator 2 – Coarse Tuner

15. Oscillator 2 – Fine Tuner

16. Mixer Circuit

17. Output Circuit

18. Software Flowchart: • Determine pitch of input • Count samples between zero crossings • Determine step size through lookup table • Different step sizes produce different frequencies • Output all 5 waveforms • However, output nothing if the input amplitude is too small • Save pointer value to remove phase error

19. Software, cont’d • Optional Tremolo effect - modulates generated waveform by 8.3Hz sine wave

20. FPAA • Subtractive Lowpass Filtering – 2nd-order, -6dB cutoff at 2.33kHz

21. FPAA, cont’d • Subtractive Bandpass Filtering, 2nd order, -6 dB cutoff at 1kHz

22. DC Filter: Removes the +2 volt DC offset generated by the FPAA -6 dB cutoff at ~30 Hz (assuming amplifier impedance of 3 kΩ) Low-Pass Filter Removes high frequency content due to FPAA’s sample-and-hold routine -6 dB Cut-off at 21.276 kHz Analog Filters

23. Results

24. Theremin Output Lowest Tone (188 Hz) 893Hz

25. DSP Outputs with FFT Sine Wave Sawtooth

26. DSP Outputs, cont’d Organ Tone Square Wave

27. DSP Outputs, cont’d Triangle Wave

28. DSP Output with Tremolo Sine Wave Square Wave

29. Tremolo, cont’d Triangle Sawtooth Organ

30. Lowpass Filtered Signals Square Wave Sawtooth

31. Bandpass Filtered Signals Sawtooth Square Wave

32. Testing Procedures • Signal-to-Noise Ratio(SNR) • Oscilloscope’s FFT function • Noise independent of signal input • Maximum-amplitude output signal used to determine SNR

33. SNR, cont’d • DSP and FPAA: SNR = 54.32 dB

34. Testing, cont’d • THD (Total Harmonic Distortion) - Unwanted harmonics in output signal - Measured using Line In on a computer to Matlab interface

35. THD, cont’d • DSP and FPAA: THD = -44 dB

36. Frequency Error Measurements Testing, cont’d

37. Testing, cont’d • Effective Bandwidth • Difference between 2 points: 1. User’s hand nearly touching antenna 2. Furthest distance between hand and antenna which produces negligible capacitance

38. Bandwidth, cont’d • Theremin • 196 Hz ↔ 3.2 kHz • DSP • 90 Hz ↔ 800 Hz • Overall • 200 Hz ↔ 800 Hz

39. Challenges • Theremin: • Faulty components • Antenna • DSP: • Availability of 32-bit processor • FPAA: • +2 V offset voltage • Tremolo implementation

40. Successes • Antenna construction • DSP implementation • LPF, Bandpass filtering using FPAA

41. Recommendations • More effects: • Reverb • Distortion • Vibrato • Different control instruments • Toggle switch array, GUI

42. Questions?