[Freeswitch-users] Tone segment f1 and f2

Hi guys What is the meaning of this (specially f1 and f2): mod_spandsp_dsp.c:705 Tone segment: f1 = -1, f2 = -1, duration = 11232 mod_spandsp_dsp.c:705 Tone segment: f1 = 1, f2 = 3, duration = 48 mod_spandsp_dsp.c:705 Tone segment: f1 = -1, f2 = -1, duration = 944 mod_spandsp_dsp.c:705 Tone segment: f1 = 2, f2 = 3, duration = 32 mod_spandsp_dsp.c:705 Tone segment: f1 = 3, f2 = -1, duration = 32 mod_spandsp_dsp.c:705 Tone segment: f1 = -1, f2 = -1, duration = 944 mod_spandsp_dsp.c:705 Tone segment: f1 = 1, f2 = 2, duration = 64