How to Check DTMF Wave?


When you have the DTMF related issue with the lines - Analog/ISDN/GSM, you need to capture the port/channel signal to check if the DTMF has been sent or received correctly.

How To

1. Capture the port signal.

Follow the right guide as per your lines.

2. Analyze the DTMF wave.

1) Use the audition tool like Audition to open the port signal capture file.

  • Sample Rate: 8000 Hz
  • Encoding: 16-bit PCM


Check the Frequency Analysis window selected.


2) Choose any DTMF wave.


3) Check the if there exists 2 noticeable frequency peaks in the Frequency Analysis window.

If yes, it means the DTMF wave should be fine.

If it is hard to find 2 peaks, then it is highly possible to have the DTMF detection problem.


4) Check the frequency of the 2 peaks.

- Low Frequency

Move the cursor to the peak, and it shows the frequency is around 781 Hz.


- High Frequency

Move the cursor to the other peak, and it shows the frequency is around 1344 Hz.


Note that the cursor might be not 100% precise. But the deviation is safe to identify the DTMF digit.

By comparing the DTMF frequency table, we found out the DTMF we analyze is digit 5.


Have more questions? Submit a request


Please sign in to leave a comment.