FPGA_projects

• Audio project
• FFT Video
• FFT Video 2048

Audio project

Simple variation of the base block design of PYNQ Z2 board. It will simply stream the audio through Vivado IPs I2S Rx-Tx (AXI stream @ 100 MHz); PYNQ audio codec will take care of the analog-to-digital and digital-to-analog conversions.

FFT VIDEO

AXI audio stream demuxed in L-channel and R-channel, 1024-point FFT (Vivado IP) is applied to both channels and finally the output magnitude is displayed on an HDMI monitor (1920x1080 @ 30Hz).

FFT VIDEO 2048

Same as the previous version with some tweaks. Only a real input is fed into the FFT and, as suggested in the vivado FFT logic core documentation, only the second half of the output is considered.
A windowing is added to lowering spectral leakage, by default no window is applied; to enable windowing it is necessary to set the selector to '1', it will multiply the input by a factor stored in a dual port RAM accessible from the notebook.
In the BRAM is initially stored an Hann-function, but is also selectable Hamming, Cosine, Gaussian and Rectangular windows or it is possible to define a custom function (via Python notebook).

It is possible to dispaly the log2 of the output. The logarithm is computed using a priority encoder and a III order taylor expasion.

FFT xilinx IP parameters:

• 2048 N-point
• Scaled (fixed point)
• 24 bit input/output width
• Pipelined/Streaming architecture
• Non real time
• Index is embedded in the TUSER axis output

Future implementation

• Video frame overlay to show the frequency axis (in the display)
• Sync FFT output ($$\sim23$$Hz) with the monitor refresh rate (30Hz)
• Find a better way to display the spectrum (now is linear in the frequencies)

Logarithmic output

This is an example of the logarithm result.

The red signal is the input and subsequently we have the Priority encoder output (yellow), I order approximation (orange), II order approximation (light blue), III order approximation (purple).

FFT output example

Actual FFT output of an input song.