Symbol		Measurement Unit
ap	cutting depth	mm
f	feed rate	mm/rev
$E_S$	sound wave pressure signal	Pa
$E_{Si}$	the measured value of the sound signal	Pa
$E_{S0}$	the measured initial value of the sound signal	Pa
${\overline{E}}_S$	relative sound signal	-
${\overline{E}}_S(\tau )$	the relative value of the sound pressure signal relative to time τ	-
$E_{Si}(\tau )$	the measured value of the sound signal relative to time τ	Pa
$E_{S0}({\tau }_0)$	the measured initial value of the sound signal relative to time τ0	Pa
${\widehat{E}}_S$	the root-mean-square value of useful signal and interference	Pa
${\widehat{E}}_{Si}$	the root-mean-square value of the measured value of the sound signal	Pa
${\widehat{E}}_{S0}$	the root-mean-square value of the measured initial value of the sound signal	Pa
${\widehat{E}}_S^{SUM}$	the total effective sound pressure value at the control point	Pa
$E_{3B}$	the magnitude of the amplitude of the sound wave	Pa
$E_{3B}(\tau )$	the magnitude of the amplitude of the sound wave relative to time τ	Pa
$E_{3B}({\tau }_0)$	the magnitude of the amplitude of the sound wave relative to time τ0	Pa
$E_{Sh}$	real-time audio signal of the cutting process response in real time	Pa
$n_{PCS}$	number of read signal values	-
$\epsilon (\tau )$	the duration of the multiplicative noise	min
$\widehat{\epsilon }(\tau )$	the root-mean-square value of the duration of the multiplicative noise	min
$\tau$	the time of the current measurement to which the quantities relate	min
${\tau }_0$	the time of the initial measurement to which the quantities relate	min
${\tau }_{Sh}$	the ESh pulse duration	10−4 s
$\Delta \tau$	PC processing time step	10−5 s
$T$	average predicted trouble-free operation time of machining systems using cemented carbide cutting tools from the current batch of samples	min
${\overline{T_{}}}_{\exp }$	average experimental time of failure-free operation/ numerical value of tool life	min
$L$	length of the bar (in terms of dynamic characteristics, equivalent to a metal object that produces a sound impulse when dropped on the floor, for example)	m
$C$	speed of propagation of longitudinal vibrations in metal	m∙s−1
$a_{qp}$	machining quality index, an indicator for adaptive control	-
$h_r$	the amount of dimensional wear in the blade tip area	mm
$h_r(\tau )$	the amount of dimensional wear in the blade tip area relative to time τ	mm
$h_r({\tau }_0)$	the amount of dimensional wear in the blade tip area relative to time τ0	mm
$\delta$	the degree of change in the geometry of the workpiece component due to tooltip wear	-
$D_{\mathsf{\Phi }}$	the actual size of the workpiece component	mm
$D_H$	the nominal size of the workpiece component	mm
$D_H^{+\Delta B}$	the nominal size of the workpiece component relative to the ΔB-value	mm
$\Delta B$	change in radial tool wear	mm
$\overline{R}a$	surface roughness of the workpiece	μm
$\overline{R}a(\tau )$	workpiece surface roughness relative to time τ	μm
$\overline{R}a({\tau }_0)$	workpiece surface roughness relative to time τ0	μm
$a_R(\tau )$	the numerical value of the roughness quality index	-