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