The graph panel shows plots of measured data, impulse responses, filter
responses, target responses and the predicted effects of the correction
filters on the measured data. The plots are split into groups of traces,
selected via the tabs at the top of the graph area.
Options that affect the appearance of the traces can be found in the View settings.
Each trace can be turned on
or off via the selection buttons at the left of the trace name. Trace names
are in the same colour as the trace itself, whilst the line style for the
trace is shown between the label and the trace's value at the cursor position.
Corrected response traces use dotted lines (the default) or a lighter shade
of the measurement trace colour according to the option selected in the View
settings.
The Freq Axis button in the toolbar toggles the frequency axis between
logarithmic and linear modes. This function is also available via a command in the
Graph menu and the associated shortcut keys.
The horizontal axis zoom buttons
zoom in or out
by a factor of approximately 2 centred around the cursor position.
The Graph Limits button
allows
desired top, left, bottom and right graph limits to be defined. A dialog pops up
in which the values are entered, they are applied as entered or by the
Apply Settings button.
The vertical axis zoom buttons zoom in and out on the Y axis.
This button, in the bottom left corner of the graph area, allows the current
graph view to be saved as a JPEG image. A dialog pops up to set the desired width of
the image (default is to be the same width as the graph).
This function is also available via a command in the
Graph menu and the associated shortcut key.
The Wizard provides a variable graphical zoom capability by either pressing and holding the middle mouse button, or pressing and holding the right button then pressing and holding the left button, and dragging the pointer.
When variable zoom is active a cross is displayed, split into quadrants allowing frequency and/or spl to be zoomed in our out depending on the mouse position. The amount of zoom is governed by how far the mouse pointer is dragged from the start position.
When the Ctrl key is pressed followed by the right mouse button a zoom
box can be drawn by dragging the mouse. Measurement cursors are shown on
the outside of the box, to zoom to the shaded area click within it. If the
shaded area is too small to zoom in to a message will indicate which dimension
is too small for zooming and what the limit is to allow zoom.
To undo the last Variable Zoom or Zoom to Area, press Ctrl+Z or select the Undo Zoom entry in the Graph menu. This will restore the graph axes to the settings they had when the right or middle mouse button was last pressed. This Undo feature can be used even if you have not zoomed, just press the right mouse button when the axis settings are to your preference then you can return to these settings (undoing any subsequent movements or control changes) by pressing Ctrl+Z.
The Filter Adjust group shows the measured data and corrected response
for the current measurement along with the target response, the response of the
equaliser filters with and without the target and the Mic/Meter and Soundcard
calibration responses (if loaded).
This graph group, in common with all groups that have a frequency axis, also shows any filters that have been defined, displaying the filter's number along the top margin of the plot at the position corresponding to its centre frequency.
The frequency response of the measurement is labelled with the measurement name
The Corrected response shows the predicted effect of the measurement's filters.
The Target trace shows the target frequency response for the
measurement, including any desired
House Curve response shape.
If a House Curve has been loaded the
symbol will be displayed by the trace value.
The response includes the Bass Management curve appropriate
to the Speaker Type selected
for the measurement. The overall level of the curve is controlled by the
Target Level.
The Filters trace shows the combined frequency response of the filters for this measurement.
The Filters+Target trace shows the frequency response of the filters overlaid on the desired Target response. Selecting the filter responses to be drawn inverted and adjusting the filters so that this curve matches the measured response will result in the corrected response matching the target.
When this box is selected the responses of the filters are drawn inverted. This is useful for graphically matching the shape of a filter to the shape of the peak it is being used to correct, when the shapes match the overall response in that region will be flat.
The Mic/Meter Cal trace shows the frequency response of the Mic calibration data (if a calibration file has been loaded via the Mic/Meter settings). If the Type has been set to C Weighted SPL Meter this curve will show the effect of C weighting (only outside the range of the calibration data file that has been loaded). The trace is not shown if cal data has not been loaded. The trace is drawn relative to the Target Level.
The Soundcard Cal trace shows the measured frequency response of the soundcard relative to its level at 1kHz (if a calibration file has been loaded via the Soundcard settings). The trace is not shown if cal data has not been loaded. It is drawn relative to the Target Level.
The Impulse graph shows the impulse response for the current measurement,
the left and right windows and the effect of the windows on the data that
is used to calculate the frequency response.
The Y axis used for the impulse response can be selected as % FS or dB FS
(FS = Full Scale) via a control in the bottom right corner.
Dashed vertical black lines show the extents of the impulse response
windows, a dashed red line shows the reference position. If the window settings
are changed the region outside the new area is shown shaded until the settings
are applied. It is best to set the Y axis to dB to adjust the windows as
it is then much easier to see where the response has decayed into the noise.
After each measurement the left window width is automatically set up. For full range measurements (and down to end frequencies of 1kHz) the width is 125ms, below that it increases to allow for pre-ringing effects of using a limited sweep range.
The impulse response is that of the whole system,
including the mic/meter and the soundcard. The mic/meter and soundcard
calibrations are only applied when calculating the frequency response.
Tip: To apply or remove a mic/meter or soundcard calibration
for a measurement after it has been taken, simply load or clear the cal data
as required and press the Apply Windows button to recalculate the
frequency response.
The impulse response may be plotted with or without normalisation to
its peak value according to the setting of the "Plot Normalised" control.
When normalised plotting is selected the peak will be at 100% or 0dBFS.
This setting applies to both the Impulse graph and the All Impulses graph.
The response may be plotted inverted according to
the setting of the "Invert Impulse" control. Note hat this has no effect
when the Y axis is set to dB FS.
The "Scale Response" control re-scales
the impulse response to achieve a desired maximum SPL figure in the corresponding
frequency response. The target peak SPL figure (in dB) is updated to reflect
the current frequency response maximum SPL whenever the "Apply Windows" button
in the IR Windows control is hit.
A property of the log sweep analysis method is that
the various harmonic distortion components appear as additional impulses
at negative time, with decreasing spacing as the distortion order increases.
For example, this plot shows spikes from distortion components up to the 8th
harmonic on a laptop soundcard loopback measurement:
Here is a similar measurement for an external USB soundcard, it is a 44.1k card rather than 48k, which
limits us to the 6th harmonic in the 1s pre-impulse period - however, only the 2nd, 3rd and 5th harmonic peaks
are evident, the 4th harmonic peak is barely visible above the noise floor (which is about 10dB lower than the
laptop card). The extended lobes after the impulse are due to the card's much lower -3dB frequency, 1.0Hz versus 22.1Hz
(note that the right side of the time axis is 2.0s in this plot compared to 0.5s in the previous plot):
This group shows LF spectral decay traces over the region from 10Hz (or the
frequency resolution for the selected window width if higher) to approximately
750Hz (for a 48kHz sample rate) or to the end of the measurement sweep if
lower. The time separation of the slices is controlled by the setting just
above the Generate LF Decay button, the width of the impulse
response section that is used to generate the slice is set by the Window
control. The corresponding frequency resolution is shown next to the window width.
The traces for each slice can be drawn as conventional lines or as filled areas, selected
by the "Fill slices" check box. The alternative views are shown below.
These Spectral Decay plots are generated by shifting the impulse response window to the right by the slice interval to generate each succeeding slice. Note that if the slice width and interval are large, fewer than 8 slices may fit within the impulse duration, in which case some slices will not be generated. The default window type for this plot is Tukey 0.25, other types may be selected via the Low Frequency Decay entry in the Analysis settings.
This group shows a waterfall plot over the region from 10Hz (or the
frequency resolution for the selected window width if higher) to approximately
750Hz (for a 48kHz sample rate) or to the end of the measurement sweep if
lower. The time span for the waterfall is controlled by the setting just
above the Generate LF Waterfall button, the width of the impulse response
section that is used to generate the slices is set by the Window control.
The corresponding frequency resolution is shown next to the window width.
Best results are obtained when the window is smaller than the time span.
The waterfall plot is generated in the same way as the Spectral Decay plots, shifting the impulse response window to the right by a proportion of the time range to generate each succeeding slice. The default window type for this plot is Tukey 0.25, other types may be selected via the Low Frequency Decay entry in the Analysis settings.
The slice slider selects which slice is at the front of the plot - as
the slider value is reduced the plot moves forward one slice at a time.
The trace value shows the SPL figure for the frontmost slice, the corresponding
time for that slice is shown at the top right of the graph.
The labels at the sides of the plot show the time axis values
The waterfall allows another measurement's plot to be overlaid on the current
measurement. The overlay is generated slice-by-slice, plotting a slice of the
current measurement's waterfall, then a slice of the overlay, then the next slice
of the current measurement and so on. N.B. before a measurement is available
to overlay it is necesary to generate the LF waterfall data for it.
Transparency can be applied to the main plot, the overlay, or both. When
transparency is set to 0%, as above, both plots are solid. If only one plot
is selected for display it is drawn solid regardless of the transparency
setting. In the image below the main plot (before acoustical treatment)
is drawn at 75% transparency, allowing the overlay (after acoustical treatment)
to show through. The transparency mode can be switched between main/overlay/both
to ease comparison between the plots.
The controls for transparency are brought up by the More Waterfall Controls
link. The More Controls dialog also has x and y sliders to alter the viewing
angle of the plot, the z slider alters the strength of the perspective effect.
This group shows the measured responses for all measurements on the same plot. The "Separate the traces" check box offsets each trace downwards from the preceding trace to make it easier to distinguish individual features when the traces are at similar levels.
The Averaging group allows the average of selected measurements to be generated. Any of the traces which are selected when the Average The Responses button is pressed will be included in the averaging. The frequency range of the average trace covers the region where all included traces have data, for example if one trace was measured to 200Hz, another to 500Hz and a third to 1000Hz the average would range to 200Hz (to the lowest end frequency).
New measurements (those made after the last average was generated) show new next to the trace value, whilst those included in the last average show avg.
Note that Average traces do not have any impulse response data so waterfall and spectral decay plots will not be available.
This group shows the predicted effects of the equaliser filters for all measurements on the same plot.
This group shows the impulse responses for all measurements on the same plot. If the "Plot Normalised" check box is selected all responses will be plotted normalised to their peak value, placing the peaks at 100% or 0dBFS.
The full range energy-time curves are displayed on this graph. The energy-time
curve is the magnitude of the analytic function whose real part is the impulse
response and whose imaginary part is the Hilbert transform of the impulse
response. The energy-time curves can be smoothed by a moving-average filter
of the selected duration.
This group shows the generated sweep test signal and the raw captured system
response as acquired via the soundcard, which may be useful for troubleshooting.
This is not a live display, it updates with new content after a sweep has completed.
Only the signals for the last measurement are shown. The Y axis is the percentage
of digital full scale. The generated sweep is shown normalised so that its peak
value is 100%. If the captured trace reaches +100 or -100% it is clipping
and the sweep level or AV processor volume should be reduced.
A check box is provided to invert the captured trace for easier comparison with the test signal if the soundcard input is inverting.