So the 'SOUND f,l' command in Qbasic is used to play a sound, where f = the frequency of the tone in Hertz (cycles per second) and l = length of the tone in seconds or milliseconds. I am trying to play two tones at one time in order to create a dual-tone multi-frequency tone (DTMF). I can only seem to play one at a time. How can I play both sounds at the same time? Example: Combining a 697 Hz tone and a 1209 Hz tone, played for for 5 seconds.