DTMF
Dual Tone, Multi-Frequency, which is the tone that’s heard with each press of a key on a touchtone keypad.
When each key is pressed on a phone, it generates two frequencies. One tone is generated from a high-frequency range of tones and the other from a low-frequency group. This means a voice cannot imitate the tones. An alternative to asking your customers to speak their card details over the phone is to ask them to type the numbers into the telephone keypad – creating these DTMF tones. These tones can be interpreted by telephony applications, bringing many security advantages, but the same tones can be converted back into real card data so it is important to secure them. The tones may also be stored in call recordings and other systems leaving these vulnerable to fraud.
Read more about DTMF masking