Macros: TraceMag, YlogTop

To better view fine details of a waveform, Spectrum, or Histogram, you may want to enlarge the displayed view.

The small up and down arrow buttons above the Y axis adjust the display magnification, or you can drag the axis up and down with the mouse. Alternatively, the PgUp and PgDn keys do the same thing and are often more convenient.

Magnification only affects the display, not the signals. It is thus not a substitute for the Input or Generator level or volume controls. For example, if an input signal is distorted because the input range is too sensitive, reducing the magnification will not change that fact.

Note that when you change magnification, the cursor readouts are not affected because the values being measured are the same. The trace display changes in size, but the Y axis also changes so that it is always correct.

Display magnification is maintained separately for different display modes, so changing the waveform magnification has no effect on the spectrum, and changing the linear Spectrum magnification does not affect the Y-log Spectrum range.

These magnification controls also affect the Spectrogram (Sgram) range (shown via a color bar at the right edge of the trace area), which is likewise independent of other modes.

For Y-log Spectrum or Sgram modes only, you can use SHIFT along with PgUp and PgDn to shift the range up or down, instead of just expanding or shrinking it. For example, the default range runs from 0 down to -90 dB. If you hit SHIFT+PgUp twice the range will be from -20 down to -110 dB. You can use the shifted and unshifted page keys to magnify any portion of the range, such as from -60 to -66 dB.

The SHIFT key doesn't allow this type of Y-axis offset in linear Spectrum or in waveform modes. However, in waveform mode there is another way to get a similar result. Normally, if you increase magnification you can see finer details near zero on the waveform; higher or lower values tend to get driven off-screen. But you can use the Zero Cursor option (Zero Cr) to shift the waveform such that the value under the solid cursor moves to zero. Then you can magnify it as much as you want, and it will always stay in the center of the screen. The Y axis is not affected by this, so you can use it to read relative distances by eye. The cursor readouts are also unaffected by Zero Cr, so they continue to read the true unshifted absolute values.

Macro Notes:

In waveform, Histogram, and linear Spectrum modes, TraceMag=0 sets the display to show the true full-scale range of the signal. Note that the full-scale range is affected by the Input Level and Generator Volume as well as Full-Scale Range, External Gain, and User Units on calibrated systems. Regardless, TraceMag=0 will set the Y axis so that a full-scale signal will just fill the trace area.

The value you supply specifies the magnification as a power of 2, so TraceMag=1 doubles the magnification, 2 = x4, 3 = x8, and so on. Note that doubling the magnification means that signals only half as large will fill the screen, so the Y-axis range is cut in half. Thus, if the waveform Y axis shows +/-1.00 at TraceMag=0, it will show +/-500m at TraceMag=1, +/-250m at TraceMag=2, etc.

You can also enter negative values to reduce the size of the trace. This is especially useful when showing Juxt Arrays of multiple traces. TraceMag=-1 will cut the magnification in half, which doubles the full-scale range shown on the Y axis.

Alternatively, TraceMag=>1 doubles the magnification from its current setting, and TraceMag=>-1 halves it.

In Y-log Spectrum or Sgram modes TraceMag sets a range number which specifies the extent of the range in dB, while YlogTop sets the top or starting dB value. For example, if you use TraceMag=14 to set the range that covers 90 dB (see table below), then YlogTop=0 specifies that this will be from 0 to -90 dB.

The TraceMag log ranges are:

• 0 = 6 dB in 1 dB steps.
• 1 = 8 dB in 1 dB steps.
• 2 = 10 dB in 1 dB steps.
• 3 = 15 dB in 5 dB steps.
• 4 = 20 dB in 5 dB steps.
• 5 = 25 dB in 5 dB steps.
• 6 = 30 dB in 5 dB steps.
• 7 = 35 dB in 5 dB steps.
• 8 = 40 dB in 5 dB steps.
• 9 = 45 dB in 5 dB steps.
• 10 = 50 dB in 5 dB steps.
• 11 = 60 dB in 10 dB steps.
• 12 = 70 dB in 10 dB steps.
• 13 = 80 dB in 10 dB steps.
• 14 = 90 dB in 10 dB steps.
• 15 = 100 dB in 10 dB steps.
• 16 = 110 dB in 10 dB steps.
• 17 = 120 dB in 20 dB steps.
• 18 = 140 dB in 20 dB steps.
• 19 = 160 dB in 20 dB steps.
• 20 = 180 dB in 20 dB steps.

As for linear modes, you can either set the range number directly, or use TraceMag=>1 to increment or TraceMag=>-1 to decrement the current range.

YlogTop sets the top of the Y axis directly in dB, rounded to the nearest step for the current TraceMag range. For example, if you use YlogTop=43 and the current TraceMag range number is 14 (90 dB in 10 dB steps), the top of the range will be rounded to 40 dB, so the overall Y axis will run from +40 dB to -50 dB. But if the current TraceMag range number is 5 (25 dB in 5 dB steps) the axis will run from +45 to +20 dB.

Note that TraceMag is independent of the current Input level, Generator volume, Full-Scale Range, External Gain, User Units, or calibration state: The range number always specifies a dB range of a particular size. YlogTop, on the other hand, does depend on these things. For example, on an uncalibrated system the dB values are relative to full-scale, so a top value of 0 dB means a maximal signal, which might represent a really loud sound. But with a calibrated system reading in dB SPL, 0 dB is near the lower threshold of hearing.

As with TraceMag you can use YlogTop=>1 to increment or YlogTop=>-1 to decrement the current top value by one label step. Note that an increment here means "more sensitive", the same as SHIFT+PgUp, which means the top value becomes smaller (more negative).

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