Segment Expressions

STx uses a special syntax to address a segment of a sound file. The syntax allows for the mixed use of segment names and time values in a complex expression known as a "segment expression". Segment expressions can be used in all commands and dialogs where a signal segment (or position/duration) can be specified (exceptions are described in the Command Reference). In dialogs, the supported value formats/types are always described in the control/dialog caption.

Segment expression

A segment expression addresses a part of a soundfile with a non-zero duration. It can consist of (1) a segment name, or (2) of two label expressions (see below) specifying the beginning and the end of the segment, or (3) of two label expressions (see below) specifying the position of the segment and its duration.

segment expression	explanation
labelexpression_labelexpression	(beginning and end)
labelexpression_+labelexpression	(beginning and duration)
labelexpression_-labelexpression	(end and duration)

Labels

A label expression is a position in a sound file (e.g. the begin/end of a segment) or the duration of a segment. A label expression may consist of a sign (+/-) and one or more values formatted as described below and combined with the operators + (add) or – (subtract). If a label expression contains blanks, it must be quoted when used as an argument.

label expression	explanation
segmentname:B	start time of segment segmentname
segmentname:E	end time of segment segmentname
segmentname:L	duration (length) of segment segmentname
numberS	time in seconds
numberMS	time in milliseconds
number	number of samples

The segment expression segexpr specifies a label (position) in a signal or a segment (part) of a signal. The command evaluates the segment expression and returns the label position or the begin, end and length of the segment.

segexpr	description
bexpr	a position (label) at bexpr
bexpr_eexpr	a segment with begin bexpr and end expr
bexpr_+lexpr	a segment with begin bexpr and length lexpr (end = bexpr+lexpr)
eexpr_-lexpr	a segment with end eexpr and length lexpr (begin = eexpr-lexpr)

Each part (bexpr, eexpr and lexpr) of the segment expression specifies a time in samples and may consist of one or more time values which are joined with the operator + (add) or - (subtract).

value	description	value in samples	comment
x	x samples	x
xs	x seconds	x * sr
xms	x milliseconds	x / 1000 * sr
xHz	periode of a signal with x Hz	sr / x
xkHz	periode of a signal with x kHz	sr / (x * 1000)
x%	x percent of the signal length	l * x / 100	usage 1 and 2 only
x%%	x per mill of the signal length	l * x / 1000	usage 1 and 2 only
segid	begin and length of the segment with id segid		usage 3 only
segid:b	begin of the segment with id segid		usage 3 only
segid:e	end of the segment with id segid		usage 3 only
segid:l	length of the segment with id segid		usage 3 only

with:	x	=	a number
	sr	=	signal sampling rate in Hz
	l	=	signal length in samples (e.g. soundfile length)
	segid	=	id of a segment defined in the xml-file item

Examples

0_4s

addresses 0 samples to 4 seconds

SegmentA:B+100_+10s

addresses 100 samples after the beginning of SegmentB for a duration of 10 seconds

SegmentB

addresses SegmentB

SegmentA:B_SegmentB:E

addresses the beginning of SegmentA to the end of SegmentB

SegmentB:E_-100ms

addresses 100 milliseconds before the end of SegmentB to the end of SegmentB

Notes: For some expressions, the values number% (percentage of the full duration) and number%% (thousandths of the full duration) can be used, but only if the 'full signal' is available/defined (e.g. for envelopes of sequence signals).A segmentname can only be used if a sound file or an audio-element of an XML-file is involved in the expression evaluation.Segment names are case sensitive!