Graph Panel

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 drop-down list at the top right corner of the graph area.
Trace Groups Selector

Note that by default the traces are drawn antialiased. This improves their appearance, but increases plotting time - to speed up plotting, uncheck the "Use Antialiasing for Traces" option in the Graph menu. The waterfall plot is also drawn with antialiasing by default and is fairly graphics-intensive, but the plot time penalty is only when scrolling the plot or changing the axis scalings. Again, to speed up plotting uncheck the "Use Antialiasing for Waterfall" option in the Graph menu.

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 current cursor position. Measured data traces use dark colours, corrected response traces use lighter shades of the same colours.
Trace Labels

Measured data traces may be smoothed by fractional octave averaging using the selector below the trace name in the Filter Adjustment trace group.
Trace Smoothing

Note that the names of the measurement channels are just labels, any channel's data can be loaded in as any trace - for example, most systems do not have an Aux channel so that can be used as an additional storage location for a set of data from another channel, or 3 sets of measured data for the Left channel using different filters settings could be loaded into the left, centre and right traces for easy comparison. The names displayed for each channel can be changed by right-clicking on the channel's tab in the filter pane and entering the new name.

Frequency Axis Log/Linear Button

The Log/Linear button at the right hand end of the frequency scroll bar 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.
Log/Linear Frequency Axis Button

Horizontal Axis Zoom Buttons

The horizontal axis zoom buttons Frequency Axis Zoom Buttons zoom in or out by a factor of approximately 2 centred around the cursor position. This function is also available via commands in the Graph menu and the associated shortcut keys.

Set Graph Extents Button

The Set Graph Extents button Set Graph Extents Button allows desired top, left, bottom and right graph extents to be defined. A dialog pops up in which the values are entered, they are applied by the Apply Settings button.
Graph Extents Dialog

Vertical Axis Zoom Buttons

The vertical axis zoom buttons zoom in and out on the Y axis.
Y Axis Zoom Buttons
This function is also available via commands in the Graph menu and the associated shortcut keys.

Save Graph as JPEG Button

Save Graph as JPEG Button 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).

Zoom control grid

This function is also available via a command in the Graph menu and the associated shortcut key.

Variable Zoom

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.

Zoom control grid

Zoom to Area

When the right mouse button is pressed 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.
Zoom to area

Undo 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.

Filter Adjustment

The Filter Adjustment group shows the measured data and corrected response for the current channel 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). It also provides access to controls that set the duration of the post-impulse window and apply the window settings to recalculate the response (see Impulse Response Controls for details). The AV processor's bass management filters are incorporated in the traces.
Filter Adjustment Graph Group

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.

Measured

The Measured response for a channel shows the measured data, either that measured by the wizard or data that has been imported.

Corrected

The Corrected response shows the predicted effect of the channel's filters.

Target Response

The Target Response trace shows the target frequency response for the current channel, 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 channel. The overall level of the curve is controlled by the Target Level.

Filters

The Filters trace shows the combined frequency response of the current channel's filters.

Filters+Target

The Filters+Target trace shows the frequency response of the current channel's 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.

Invert Filters

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.

Mic/Meter Cal

The Mic/Meter Cal trace shows the frequency response of the Mic calibration data (if a calibration file has been loaded via the Meter menu option). If the option to Compensate for C Weighting has been selected 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 disabled if cal data has not been loaded. The trace is always drawn vertically centred in the graph window.

Soundcard Cal

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 Meter menu option). The trace is disabled if cal data has not been loaded. The trace is always drawn vertically centred in the graph window.

Impulse Response Controls

The Impulse Response Controls group shows the impulse response for the current channel, the pre and post-impulse windows and the affect 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 dBFS (FS = Full Scale) via a control in the bottom right corner of the graph area.
Impulse Response Y Axis Selector

There are controls to re-scale 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 is hit.
Scale Impulse Response Controls

There are also controls for the durations of the pre and post impulse windows, the reference position about which they are centred, and a button to Apply the windows and recalculate the frequency response. Dashed vertical black lines show the extents of the window, a dashed red line shows the reference position. If the settings are changed the region outside the new area is shown shaded until the settings are applied. The frequency resolution corresponding to the total window duration is shown above the Apply Windows button - the longer the duration, the higher the resolution. Alternative window shapes may be selected via the Analysis menu entries. ETF users should note that ETF gate times are specified in a different manner, to convert an ETF gate time to the approximately equivalent window width, multiply by 1.4.
Impulse Response Controls

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.
Impulse Response dB Scale

After each measurement the pre-impulse window width is automatically set up. For full range measurements (and down to end frequencies of 1kHz) the width is 10ms, below that it increases to allow for pre-ringing effects of using a limited sweep range. 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:
Impulse Response with Harmonic Peaks

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):
Impulse Response with Harmonic Peaks

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 full range energy-time curve may be displayed in place of the impulse itself (this 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 curve can be smoothed by a moving-average filter of the selected duration.
Energy-time curve controls
Energy-time curve

Low Frequency Spectral Decay

This group shows spectral decay traces over the region from 10Hz 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 Spectral Decay button, the width of the impulse response section that is used to generate the slice is set by the Window Width control. The corresponding frequency resolution is shown in square brackets.

Low Freq Spectral Decay Controls

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.
Low Freq Spectral Decay, normal traces
Low Freq Spectral Decay, filled traces

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 menu.

Low Frequency Waterfall

This group shows a waterfall plot over the region from 10Hz 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 Waterfall button, the width of the impulse response section that is used to generate the slices is set by the Window Width control. The corresponding frequency resolution is shown in square brackets.
Low Freq Waterfall

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 (and the Spectral Decay plot) is Tukey 0.25, other types may be selected via the Low Frequency Decay entry in the Analysis menu.

The x and y sliders alter the viewing angle of the plot, the z slider alters the strength of the perspective effect. 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 in the trace label.

Low Freq Waterfall Controls

The waterfall allows another channel's plot to be overlaid on the current channel. The overlay is generated slice-by-slice, plotting a slice of the current channel's waterfall, then a slice of the overlay, then the next slice of the current channel and so on.
Low Freq Waterfall Overlay

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.
Low Freq Waterfall Overlay

Measured Responses

This group shows the measured responses for all channels 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.

Measurement Averaging

The Measurement Averaging group allows the average of selected measurements in the Left, Right, ..., Sub channels to be generated and placed in the Aux channel. Any of the traces which are selected when one of the Average buttons is pressed will be included in the averaging, provided they have suitable data - only traces with Impulse Response data can be included when averaging impulse responses. The frequency range of the average trace covers the region where all included traces have data, for example if one trace was measured between 10 and 200Hz, another between 20 and 500Hz and a third between 15 and 1000Hz the average would cover 20 to 200Hz (from highest start to lowest end).

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.

Measurement Averaging Controls

To average measurements from multiple positions, make each measurement in a different channel and use Average Frequency Responses to generate the average. Note that the resulting trace will not have any impulse response data so waterfall and spectral decay plots will not be available.

Average Impulse Responses should only be used for averaging multiple measurements from the same location, it is likely to produce invalid results if used on measurements made at different locations. Averaging measurements taken on all 8 channels gives a signal-to-noise ratio improvement of around 9dB, however any interference tones or constant frequency background noises (which appear as peaks in the waterfalls which do not decay) will typically be reduced by more as their phases in different measurements will differ and their summation will lead to varying degrees of cancellation.

Impulse response averaging is only allowed for impulses which have the same length and the same sampling rate (all Wizard sweep measurements made at the same soundcard sample rate satisfy this requirement).

Predicted EQ'd Responses

This group shows the predicted effects of the equaliser filters for all channels on the same plot.

Impulse Responses

This group shows the impulse responses for all channels on the same plot, along with the window trace for the currently selected channel and a check box to show only the windowed data for the currently selected channel.

Oscilloscope

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 measurement level or AV processor volume should be reduced.
Oscilloscope Plot

A check box is provided to invert the captured trace for easier comparison with the test signal if the soundcard input is inverting.

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