ECE303L Signals and Systems Lab 7
- Investigate the use of MATLAB in decoding touchtone sound
- Study the effect of noise on the accuracy of decoding sound
- Build a Sallen-Key filter to detect one of the touchtone
frequencies (and reject the others).
- The example script
decodes DTMF sound sequences such as
random.wav (which was produced
Run the script on
phone.wav and report the telephone
- Run this script on the phone numbers you generated in lab 6. You may
modify the script as necessary, but it should continue to work on the
original sound sequences.
- Study the effect of additive white noise (uniform random
values) on the accuracy of the MATLAB decoder. Include the response of
the decoder to pure noise. Determine the signal-to-noise ratio
required for accurate decoding (no errors). Adjust the relative levels
of signal and noise so that the rms-value of the signals remain
- Build a bandpass Sallen-Key filter (you may need to follow it with a
voltage divider) to detect any one of the touchtone frequencies and
reject the others. Add a circuit to respond by lighting an LED when
the frequency is detected.
- Build a live decoder by using the data acquisition system (or
the winsound driver on your laptop) to acquire a live phone number
(from your cell phone) and MATLAB to decode the telephone number.
Maintained by John Loomis,
last updated 22 Nov 2010