Data AcQuisition And Real-Time AnalysisScope - Spectrum - Spectrogram - Signal Generator
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Macros: TraceMag, YlogTop, YlogScrnTop, YlogScrnBot
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. The PgUp key magnifies and PgDn shrinks the display; in Y-log Spectrum mode, PgUp takes you to a more-sensitive range (more dB from top to bottom), which causes the displayed signal to move up-screen, while PgDn does the opposite.
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.
In addition, Y-log Spectrum and Sgram/PT ranges allow the use of CTRL+PgUp to increase the range in 1 dB steps, and CTRL+PgDn to decrease by the same amount. For really fine control, ALT+PgUp and ALT+PgDn move in 1/16 dB steps. (You will rarely need either of these fine controls; just be aware that they are available for special cases.)
Note that the standard Y-log Spectrum and Sgram/PT ranges include "headroom" of 1/15 of the nominal range, such that the 0 to -90 range actually extends to +6 dB above the 0 dB line, the 0 to -45 dB range extends to +3 dB, etc. See the list under Macro Notes, below.
For Y-log Spectrum or Sgram/PT 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.
SHIFT+CTRL along with PgUp or PgDn shifts by 1 dB steps, while SHIFT+ALT shifts by 1/16 dB steps. As for the unshifted CTRL and ALT fine controls mentioned above, these are only likely to be needed in special cases.
The exact top and bottom dB range values are displayed to the right of the trace area in Y-log Spectrum and Sgram/PT modes. These controls can also be used to enter specific limits for special purposes. If you do this, always enter the top value first, since that slides the overall range up or down and thereby changes the bottom value, but changing the bottom control doesn't affect the top.
Since these controls are seldom needed, they are typically hidden by any control dialog (such as the default Generator dialog) that happens to be open. You can close any such dialog, or drag it to one side, in order to view the range extents.
The SHIFT key doesn't allow Y-axis shifting 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 Screen Zero option to shift the waveform such that a point of interest moves to zero. Toggle Screen Zero on via the Zero button in the toolbar (or ALT+Z), then move the solid cursor to the point of interest and hit ALT+SHIFT+Z to shift the waveform so that point is vertically centered.
Then you can magnify the trace as much as you want, and the location of interest 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 Screen Zero, so they continue to read the true unshifted absolute values.
Hitting SHIFT+Home at any time will restore the default full-scale range for waveform and linear Spectrum modes. In Y-log Spectrum or Spectrogram modes, it restores the full-scale top of the Y-axis if it had been previously shifted via SHIFT+PgUp or SHIFT+PgDn, but does not change the overall range extent (difference in dB between top and bottom).
In waveform, Histogram, and linear Spectrum modes, TraceMag=0 sets the display to show the true full-scale range of the signal, the same as hitting SHIFT+Home. 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/PT 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.
Note, however, that these are the label ranges; the actual display includes "headroom" of 1/15 of the nominal range, such that the 0 to -90 range actually extends to +6 dB above the labeled 0 dB line. Using YlogTop shifts the effective 0 dB line, but the headroom is still included. If you use YlogTop=-20 on this range, for example, the labels will run from -20 to -110 dB, but the +6 dB headroom means that the region above the -20 line extends to -14 dB. You can read or set this top value with YlogScrnTop, as discussed below.
The TraceMag log ranges are:
0 = -6 dB in 1 dB steps, +0.40 dB headroom 1 = -8 dB in 1 dB steps, +0.53 dB headroom 2 = -10 dB in 1 dB steps, +0.67 dB headroom 3 = -15 dB in 5 dB steps, +1.00 dB headroom 4 = -20 dB in 5 dB steps, +1.33 dB headroom 5 = -25 dB in 5 dB steps, +1.67 dB headroom 6 = -30 dB in 5 dB steps, +2.00 dB headroom 7 = -35 dB in 5 dB steps, +2.33 dB headroom 8 = -40 dB in 5 dB steps, +2.67 dB headroom 9 = -45 dB in 5 dB steps, +3.00 dB headroom 10 = -50 dB in 5 dB steps, +3.33 dB headroom 11 = -60 dB in 10 dB steps, +4.00 dB headroom 12 = -70 dB in 10 dB steps, +4.67 dB headroom 13 = -80 dB in 10 dB steps, +5.33 dB headroom 14 = -90 dB in 10 dB steps, +6.00 dB headroom 15 = -100 dB in 10 dB steps, +6.67 dB headroom 16 = -110 dB in 10 dB steps, +7.33 dB headroom 17 = -120 dB in 20 dB steps, +8.00 dB headroom 18 = -140 dB in 20 dB steps, +9.33 dB headroom 19 = -160 dB in 20 dB steps, +10.67 dB headroom 20 = -180 dB in 20 dB steps, +12.00 dB headroom
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 Y-log 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).
YlogTop=>0 has the same effect as SHIFT-Home to restore the full-scale top of the Y-axis if it had been previously shifted, but does not change the overall range extent.
YlogScrnTop sets or returns the dB equivalent to the top pixel in the trace area in Y-log mode. This is the value displayed in the control to the upper right of the trace area (typically covered by any open control dialog).
Note that unlike YlogTop this is not the label value (which is an integer, and may not be at the very top of the trace area) but the actual top pixel dB, including headroom, and may include a fractional part with 16-bit (4 decimal place) resolution.
Likewise, YlogScrnBot sets or returns the the dB equivalent to the bottom pixel, and may also include a fractional part. It is displayed to the lower right of the trace area.
If you are trying to set a specific dB range, you should always set YlogScrnTop first. Then set YlogScrnBot, which will maintain the top setting.
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