PPM

Level meter (PPM). This atom is used for the level display in the recorder application.

[SPU PPM X TYPE T UNIT REF SIZE OUT Y M P]

input	description	data type	value type	default value
X	input signal	number, vector	variable
TYPE	measurement method (HOLD, EXPONENTIAL, RMS)	number (int.), string	constant	0 (= HOLD)
T	measurement time constant in samples	number	constant	100
UNIT	output value and unit (VALUE, SQUARE, RATIO, DB)	number (int.), string	constant	0 (=VALUE)
REF	reference value, used for UNIT values RATIO and DB	number	constant	0
SIZE	length of bar (graph) used for ppm display	number	constant	100
output	description	data type	value type	comment
Y	ppm value	number	variable
M	maximum Y	number	variable
P	ppm bar position, always computed for the ppm value in dB (independent of UNIT)	number	variable

Description

The level meter value v_t (t = sample index) is computed for each value x_t of the input signal X. The last v_t of an evaluation cycle is used to update the outputs Y and P.

TYPE	computation of vt
0 or HOLD	vt=max⁡(|xt|,|xt−1|,..,|xt−T+1|)
1 or EXPONENTIAL	vt=max(|xt|,vt−1.k), with: k=12T
2 or RMS	rt=(rt−1.(T−1)+x2)T vt=2.rt

The last value v_t of an evaluation cycle is converted to the selected UNIT and stored in the output Y.

UNIT	Y
0 or VALUE	vt
1 or SQUARE	vt2
2 or RATIO	vtREF
3 or DB	20.log10vtREF

The output P is set to a value in range 0 to SIZE and can be used to display a level bar. For P always the logarithmic value (level in dB) is used. The level interval -140dB to 0dB is mapped to the position interval 0 to SIZE using a non-linear mapping function.

The output M is the maximum of all computed v_t values converted to the selected output unit.

See also

<SP-atoms>