Segment Expressions

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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 specifying the beginning and end or (3) two label expressions specifying a position and the duration.
segment expression explanation
labelexpression_labelexpression (beginning and end)
labelexpression_+labelexpression (beginning and duration)
labelexpression_-labelexpression (end and duration)
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



addresses 0 samples to 4 seconds


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


addresses SegmentB


addresses the beginning of SegmentA to the end of SegmentB


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!