The document discusses ECG signal compression using Fast Fourier Transform (FFT) to facilitate the transfer of ECG signals by reducing their amplitude and frequency. The compression process involves five stages: input signal, two compression counters, recovery using Inverse FFT (IFFT), and error checking. It emphasizes the importance of compression ratio and its applications in medical contexts, such as transmitting patient reports between doctors.

1. ECG
COMPRESSION
USING FFT

2. ECG
The ECG (electrocardiogram)is a diagnostic
tool that is routinely used to assess the
electrical and muscular functions of the heart.
Sometimes it is required to send the ECG
signals from one place to another place. The
ECG signals are compressed at first to reduce
the amplitude and frequency and then
transferred.

3. FFT
• ECG signals are compressed by using many
techniques. One of the most important
technique is FFT.
• FFT (Fast Fourier Transform) is a
technique used to convert analog signal to
digital signal.

4. FFT

5. Five Stages
 In FFT, The total process takes five steps:-
1) Input signal
2) Compression (counter A)
3) Compression (counter B)
4) Recovery of the original signal by using IFFT
5) Error checking

6. First stage
The input signal (ECG SIGNAL) IS TAKEN

7. Compression stage
(counter A)
 There are two stages for compression. In first
stage of compression there is a counter A. It
identifies the non-zero values of the signal
before compression.
 After compression length of the compressed
signal is compared with the length of the
actual signal.

8. ZERO PADDING
• If the length of the compressed signal is less
than the length of the actual signal, then zero
padding is done to make equal the lengths of
compressed and actual signal.

9. ZERO PADDING

10. COMPRESSION STAGE
(COUNTER B)
• Now the signal is passed through the counter
B. It identifies the non-zero values after the
compression of the signal.
• After compression length of the compressed
signal is compared with the length of the
actual signal

11. TRUNCATION
Now after compression if the
length of the compressed signal is greater
than the length of the actual signal, then
TRUNCATION of the signal is done.

12. TRUNCATION

13. COMPRESSED ECG SIGNAL

14. Recovery of the original signal by
using IFFT
Now by applying IFFT
(Inverse Fast Fourier Transform) the original
ECG signal is recovered.

15. Recovery of the original signal by
using IFFT

16. ERROR CHECKING STAGE
The recovered signal y’(t) is compared with
the original signal y(t).
Error is given by
e(t)=y(t)-y’(t)
e(t)=error in the recovered signal
y(t)= original signal
y’(t)=recovered signal

17. ERROR CHECKING STAGE

18. The compressed signal contains only positive values

19. Compression Ratio
• Compression ratio is given by
• CR=((B-A)/B) *100
• CR-Compression ratio
• A-compression in counter A
• B-compression in counter B
• Compression ratio is a major factor to
determine how much compression the signal
undergoes.

20. Applications
It finds application in
hospitals, when a patient’s report is to be
send to another doctor in prenominal place.