1. Real-Time Speech Pitch Shifting on an FPGA
Habib Estephan
Scott Sawyer
Dan Wanninger
Dr. Kevin Buckley, Advisor

2. Project Objective
To design and implement a high quality speech pitch shifter on an FPGA that allows real-time microphone input and speaker output.

3. Digital Signal Processing and FPGAs
Improved performance and flexibility over DSPs and other dedicated microprocessors
More economical than custom ASICs for low-cost or low-volume applications
Abstract design tools significantly simplifiy programming over conventional HDLs

4. SSB Frequency Shifting
Single sideband frequency shifting is a linear shift of the spectral components of a signal using the Hilbert Transform.
It does not preserve the harmonic nature of sound, and the result is of low quality.

5. Time Domain Algorithm Synchronized Overlap-Add Method (SOLA)
Pitch estimation is required to identify individual periods
Inserting/Removing periods in order to stretch/compress signal
Resampling restores the original length while altering the pitch

6. Time Domain Algorithm
Sample Audio:
Original
Up Shifted
Down Shifted

7. Time Domain Algorithm

8. Frequency Domain Algorithm
Windowed FFTs taken and IFFTs offset to time shift input
Phase terms adjusted to remove discontinuities
Time shifted signal resampled to alter pitch
Higher fidelity but increased complexity

9. Frequency Domain Algorithm
Sample Audio:
Original
Up Shifted
Down Shifted

10. Simulink and Xilinx System Generator

11. Up Pitch Shifter

12. Achievements and Deliverables
Two high fidelity algorithms simulated in MATLAB
Successful real-time FPGA implementations of the time domain approach