The most commonly used features of Scream! are accessed through Waveview windows. You can open as many Waveview windows as you like, on any combination of streams; the same stream can be part of several Waveview windows at once, at several different scales.
To open a Waveview window from Scream!'s main window:
select Window → New Waveview Window... from the main menu;
double-click on a stream ID in the streams list;
right-click on a stream in the list and select View; or
make a selection of streams and double-click the selection (or press ENTER.)
You can add further streams to the Waveview window by selecting them from the streams list and dragging the selection into the Waveview window, or by dragging them from other Waveview windows. Dragging with Ctrl held down will copy the stream from one window to another; otherwise, the stream will be moved to the new window.
If you are running Scream! in real-time mode, and you double-click on a GCF file to view it (or open the Scream! viewer in some other way), you will have both real-time and view windows open. In this case, you can drag streams from real-time windows to other real-time windows, but not from these to view windows, or from view windows to other view windows. This is because the windows are handled by different instances of the Scream! program.
You can also drag streams within a Waveview window to reorder them. (If you have paused a Waveview window with the 
icon, you will need to drag from the panel on the left, since dragging across the window will zoom in; see below.)
To the left of the stream display is a panel identifying the stream by its System ID and Stream ID, or another label if you have set one (see “Stream mapping“ on page 44.) If the label is too long to read, you can resize the panel by dragging its edge across the Waveview window. You can also hide the panel this way.
Above the stream display is a toolbar, containing icons which act on all of the streams within the window.
To zoom in and out vertically, click the vertical scale icons 
at the top left of the window, or use your mouse wheel. The current zoom factor is shown between the icons, as a ratio of pixels to counts. Zooming in and out affects every stream in the window.
To zoom in and out horizontally, click the horizontal scale icons 
, or hold down SHIFT whilst turning your mouse wheel. The current zoom factor is shown between the icons, in pixels per second. To convert to pixels per sample, divide the zoom factor by the sample rate for the stream.
If you have a large window which takes some time to scroll, especially at a high horizontal zoom factor, Scream! may not be able to finish drawing new data before it needs to scroll again. If this happens, Scream! will delay scrolling until it can display in real time once more. To prevent this, decrease the time scale.
If you have paused the window with the icon, you can zoom into an area of interest by dragging a rectangle across the streams. Scream! displays the time span in the top right corner of the rectangle, and the number of counts in the bottom left corner. When you zoom this way, Scream! will always keep the edges of the window at 1-second boundaries. You can drag across one stream, or several; the resulting window will still include all streams.
Whilst the window is paused, you can also zoom in and out by dragging the ends of the horizontal scroll bar, at the bottom of the window.
Click the Time Cursors or Ampl Cursors button to display a pair of vertical or horizontal cursors. Each cursor has a square at one end, which can be dragged across the Waveview window to measure features. If two cursors coincide, you will only be able to see the squares.
The distance between the cursors is given in the text of the Time Cursors or Ampl Cursors icon, in seconds and Hz or counts. You can have both vertical and horizontal cursors active at the same time. Because the limit of accuracy of the cursors is one pixel, you should zoom in to the range of interest before measuring.
The Ampl Cursors measure distances in counts according to the current zoom settings. However, if you have applied a scaling factor to an individual stream (see below), the Ampl Cursors do not take this scaling into account, so the measured distance will no longer be in digitizer counts.
To obtain the true value in counts, divide the value displayed in the Ampl Cursors icon by the scale factor for that stream, as displayed beneath its ID on the left-hand panel.
If a stream is shown with a physical unit (e.g. nm/s), Scream! has scaled it so that the Ampl Cursors display a value in that unit. To do this, Scream! needs to know the sensitivities of your digitizer and instrument (see Section 2.8, page 19.)
To print the data currently being displayed in the Waveview window, click on the Print icon 
. Scream! will use the current printer settings to print a full page view of the window, using the current amplitude and time scaling, filtering and other display options. You can print at any time, in either real-time or paused mode.
To print the same data in black and white (on a colour or greyscale printer), click on the arrow beside the Print icon and select Page Print (monochrome) from the drop-down menu. Black and white output is more suitable for copying or faxing.
You can also set up Scream! to print automatically, or send data directly to a connected plotter. For full details on the printing options available in Scream!, see Chapter 9, page 107.
Filtering
Clicking the Filter icon 
makes Scream! apply a filter to each of the displayed streams. This is most useful when long-period signals are causing the baseline to vary.
Click the icon again to remove the filter.
Scream! can be configured to apply different filters to each WaveView window. To select the filter, click on the arrow beside the Filter icon. A drop-down menu will appear:
Select Default filter to apply Scream's built-in FIR bandpass filter. The properties of this filter depend on the sample rate of the stream. Data at 1 or 2 samples/s is filtered with a 10 – 30 s pass band, whilst data at other sample rates is filtered with corner frequencies at 0.1 and 0.9 times the Nyquist frequency of the stream. For example, the pass band for the filter applied to a stream at 100 samples/s will be 5 – 45 Hz.
Select Custom filter to activate the filter you have designed. If you have not designed a filter, a 10 – 30 s pass band filter will be used for all sample rates.
Select Design... to open the Filter Design window (see Section 3.3, page 37.)
If you have saved some filter designs as presets, they will be listed below Design.... Select an entry to switch to a Custom filter with these settings.
If you have saved some filter designs as presets, a Delete preset submenu will also appear. Select an entry in this submenu to delete that filter design.
Click the Pause icon to stop the window scrolling. If new blocks arrive which contain data from the time period displayed, Scream! will add them to the window.
Whilst a window is paused, you can:
Scroll the waveform to left and right to view all the data that Scream! has in memory. Alternatively, hold down CTRL whilst turning your mouse wheel to scroll through the data. Because new data is still being added to the memory buffer, the scroll bar will move slowly to the left as long as the display is paused.
Zoom in and out to examine features in the data.
Select data from several streams by holding down SHIFT and dragging:
If the region you have selected is entirely filled with contiguous data, the selection is shown as a solid block. If there are gaps or overlaps in any stream, the selection is shown in a hatched style.
Select data from two streams by holding down CTRL and dragging from one to the other.
Save data to a file by selecting one or more streams (using either of the methods above) and choosing Save...:
Select the directory and format for the file, and click OK to save the data with one file for each stream (using the format shown.)
Some formats support multiple streams per file. For these formats, you can select Single File to combine the streams.
The number at the top left of the selection is the number of samples from each stream that you have selected.
Use data in a filter design by selecting a single stream and choosing Use in Filter Design... from the pop-up menu. See Section 3.3, page 37, for details.
Pass data to a Scream! extension by selecting one or more streams (using either of the methods above) and choosing the extension from the pop-up menu. See Chapter 11, page 118, for more details.
Click the Pause icon again to return to real-time mode. If you have changed the zoom settings, the window will return to its previous state, with the window once more following the real-time data.
Click the Block Boundaries icon 
to display a dotted line at the end of every GCF block displayed in the window:
The number beside each line is the number of bits used to store each sample in the block. A fixed-length GCF block with 8-bit samples (which can encode differences up to ±127 counts) can store 4 times as many samples as a block using 32 bits for each one (encoding differences as large as ±4,294,967,296 counts). Clicking the icon again removes the block markers.
Click the Zero Streams icon 
to set the offset of each stream in its “lane” so as to centre its mean value over the time period displayed. If you do not want a particular stream to be zeroed when you click this icon, right-click on the stream beforehand and select Locked Offset. This option is particularly useful when first setting up an instrument, since its output is often offset by a constant DC voltage.
When Scream! is used as a data viewer, the Pause icon is replaced with a Restore View icon 
. Click this icon to reset the time and amplitude zoom settings to their initial values, i.e. to display the entire selected data set within the window.
Right-clicking inside a Waveview window brings up a context-sensitive menu in two sections. The upper section of this menu contains options which affect a particular stream (see below.) Options in the lower section affect the whole window:
Select Background Colour... to change the background colour for the window.
Select Label... to change the title of the window. This also changes the name of the window's entry in Scream's Windows menu, and is used on printouts (see chapter 9, page 107.)
Select Clear Window to remove all streams from the window. This does not remove the streams from memory; you can retrieve them by dragging from Scream's main window onto the now-empty Waveview window.
Select No Caption to remove the title decoration and toolbar from the window. To maximise the screen area occupied by streams, first maximise the Waveview window, then choose No Caption. You can still use the mouse wheel or keyboard shortcuts (see Chapter 12, page 121) to perform the actions of icons on the toolbar.
Select Duplicate to open a new Waveview window identical to the current one. (If you have renamed a stream using Stream Name Mapping, the new window will use the new name.)
Select Overlay Streams to draw all visible streams in the middle of the window, overlaid one on top of another.
This is useful if you want to compare event records from several instruments in an array. Select the Overlay Streams option again to return to the normal display settings.
There are also several actions you can perform on individual streams, which can be accessed from the context-sensitive menu. Each stream has its own “focus lane”, although large signals or high zoom factors may make the trace extend outside the lane.
When you move the mouse pointer over a lane, a selection box is drawn around the corresponding stream's label in the panel to the left. Right-clicking will bring up the menu options for this stream.
If you have selected Overlay Streams for the window, the focus lanes are still present even though the streams are not drawn inside them. Right-clicking in the window anywhere to the right of a stream identifier will bring up the context menu for that stream.
Every stream is identified in its icon in the left-hand panel. For more details, right-click on the stream. The topmost option in the menu displays the full network path to the instrument, including its System ID and Stream ID:
Here, a stream from a digitizer with the System ID BHOLE has a mapped name of Z (see “Stream mapping”, page 44.) Right-clicking on the stream shows that the true Stream ID is DA62Z2, and that it comes from a GCF file with the name da62z2_20060112_1900z.gcf.
Selecting this option brings Scream!'s main window to the front, with the digitizer and stream selected.
Changing the appearance of streams
To change the colour of a stream's trace, right-click on the stream in the Waveview window and choose Colour.... Select the colour you want to use and click OK.
You can also set up Scream! to use particular colours automatically according to the name of the stream, and to label them differently in the Waveview window. See “Stream mapping”, page 44, for more details.
To scale an individual stream, right-click on it and select Scale...:
Enter the new scale factor and click OK. You can scale whole instruments at a time by checking the Copy to all....components in this window box. This overrides any previous scale factor active for those streams.
If you have configured Scream! to scale streams to physical units, this box will display the scale factor Scream! is using. If you enter a different scale factor, it will override the factor Scream! has chosen. To return to physical units, delete the stream from the window and restore it by dragging from Scream!'s main window.
Viewing offsets, ranges and averages
To see the range and average value for a stream, right-click on it and select Details.... A small window will appear beside the stream giving the current offset, mean, maximum and minimum values for the data in the window, together with the Diff (difference between minimum and maximum values) and Buffer (storage space taken up by this stream in memory.) The values are scaled according to the current scale factor for the stream, or to any physical unit you have selected.
To alter the offset of a stream, type a new value (in counts) into the Offset box and press ENTER. You can do this even if the stream is locked. The offset is changed for the current Waveview window only.
If you move a Waveview window, all its Details windows will move with it. You can change their relative position by dragging the title bar of each Details window.
Whilst the Details window is open, the mean value is displayed as a dotted horizontal line, whilst the maximum and minimum values are displayed as solid lines.
You can also change the offset of a stream with the keyboard. With the mouse over the Details window, pressing the ↑ and ↓ arrow keys moves the current stream up or down by one pixel, whilst Page Up and Page Down move the stream by the width of one “lane”. This feature lets you compare streams by placing one directly on top of another. The lane used for selecting the streams stays the same.
Scream! can perform real-time spectral analysis on incoming data. To enable this feature, right-click on the stream of interest in the Waveview window and choose Spectrogram from the pop-up menu.
The vertical axis of the spectrum is linear, with the Nyquist frequency (= half the sample rate) at the top and 0 Hz (DC) at the bottom. The colouring is logarithmic, giving a large total range whilst retaining sensitivity at low signal levels.
The width of the spectrum can be changed in the Display options pane of the Setup window. Pressing the + and – keys adjusts the colour contrast of the spectrogram.
The Filter Design window allows you to alter the appearance of streams in Waveview windows by applying low-pass, high-pass or band-pass filters. Each Waveview window can have its own Filter Design settings.
To open the Filter Design window, click on the arrow to the right of the Filter icon and select Design... from the drop-down menu.
From top to bottom, the window contains
the parameters of the current high-pass (red) and low-pass (green) filter in numerical form,
a graph of the response of the current filter, showing the –3 dB level and corner frequencies,
(at bottom left) display settings for the graph, and
(at bottom right) control buttons for the window.
Filter parameters
The filter parameters are shown at the top of the Filter Design window.
Select Highpass to switch on the high-pass filter, and enter the value of the corner frequency required in either the Hz or the Secs (seconds) box. You are not allowed to enter a value of 0 in either box.
While the cursor is in one of the frequency boxes, pressing the + and – keys will nudge the corner frequency up and down.
Alternatively, change the corner frequency by clicking on the graph with the left mouse button. If the low-pass filter is active, and you click to the right of the low-pass corner, both frequencies will be moved.
If the frequency you want is not shown in the window, it may be above the Nyquist frequency for the currently-selected sample rate. Change the value in the n sps box at the bottom left and try again.
Change the order of the filter by entering a number in the nth Order box.
Select Lowpass to switch on the low-pass filter, and enter the value of the corner frequency required in either the Hz or the Secs (seconds) box.
Alternatively, change the corner frequency by clicking on the graph with the right mouse button. If the high-pass filter is active, and you click to the left of the high-pass corner, both frequencies will be moved.
Change the order of the filter by entering a number in the nth Order box.
To create a band-pass filter, select both Highpass and Lowpass. Enter values into the text boxes, or click in the graph with the left and right mouse buttons to set the two corner frequencies.
When both filters are active, the individual filters are shown on the graph in light blue.
Enter a value in the Gain (dB) box to change the gain of the filter.
In the example above, the overall gain of the band-pass filter has been set to 10 dB. This is done by applying a 5 dB gain to each of the component filters. As a result, the light blue traces appear 5 dB below the dark blue trace.
Viewing spectra
You can overlay the power spectrum of up to 2 streams on the frequency graph. This is intended to help you design filters for specific events by focussing on the frequencies at which the event has significantly more energy than the background noise.
To design a filter for a specific event:
View the relevant stream in a Waveview window and click the Pause icon. Zoom in to a time period where the stream is quiet.
Holding down SHIFT, select a single stream across this quiet time range. Choose Use in Filter Design... from the drop-down menu. The Filter Design window will appear, with the spectrum of the background noise overlaid.
If you do not see the Use in Filter Design... option, check that only one stream is selected.
Leaving the Filter Design window open, switch to the Waveview window and view the event of interest.
Holding down SHIFT, select data from the same stream during an event. Choose Use in Filter Design... from the drop-down menu. A dialogue box will open asking you if you want to replace the previous spectrum or add to it.
Click Yes. The spectrum of the event will be overlaid on the background noise spectrum, in a lighter shade.
You can now click in the graph to move the filter's corner frequencies to suit the event.
If you want to view the spectrum of a different event, follow steps 3 – 4, choosing Yes when you are asked if you want to overlay the spectra. The old event spectrum will be replaced with the new one.
If you want to change the background spectrum, follow steps 1 – 2 and choose No when you are asked if you want to overlay the spectra. The old event spectrum will be erased, and the background spectrum will be replaced with the new one. Now follow steps 3 – 5 to overlay the spectrum of events as desired.
Display options
The icons at the bottom left of the Filter Design window change the properties of the graph.
The Log/Lin selection box allows you to choose a logarithmic or linear time axis. (The magnitude axis is always displayed in dB, and is therefore logarithmic.)
Enter a value in the n sps box to display a time range suitable for streams at that rate. The graph displays a 4-decade frequency range, up to the Nyquist frequency (i.e. half of the sample rate.)
When power spectra are being displayed on the graph, there is an additional selection box to the right of the Log/Lin icon.
The power spectrum calculation uses the Welch averaging periodogram algorithm. This algorithm produces frequency graphs by splitting the range into windows of a certain size. You can alter the size of window used by changing the value in this selection box.
Using a smaller window size produces a smoother graph, at the expense of losing information about lower frequencies. To examine lower frequencies, you will need to increase the window size; however, doing this will increase the noise visible at high frequency.
Presets
When you are happy with your filter design:
Click OK to apply the filter to the Waveview window and close the Filter Design window.
Alternatively, click Apply to apply the filter and leave the Filter Design window open.
Checking the Auto-Apply check box makes the Filter Design window apply immediately any changes you make to the filter. Since applying a filter may take some time, you should not check Auto-Apply if you are viewing a large amount of data.
To save the design in Scream!'s configuration file, click Save, and enter a name for the filter. You can now select the filter from the drop-down menu next to the Waveview window's Filter icon.
There are a number of Scream! setup options which affect how Waveview windows are displayed.
To change default display options for new Waveview windows, choose File → Setup... from the main menu and click on the Display tab.
Stream Buffering : You can change the size of Scream's stream buffer by altering the value and unit in these boxes. Scream! will discard any data older than this. If you want to record data to your computer's hard disk, you should use the Recording and Files panels; when you enable recording on a stream, any data in the stream buffer will be included in the recorded files. Scream! can also play back recorded GCF files (see Chapter 8, page 90.)
Status Font : Click Select... to change the font used in status streams. The change comes into effect on new and existing Status windows as soon as you click OK or Apply.
Waveview Defaults : Allows you to take the default properties for new Waveview windows from a window already on the screen. Click Select and then on the window you wish to copy. When you click OK or Apply, new Waveview windows will have the same horizontal zoom factor, filter and block boundary options, background colour, and time/amplitude cursor state as are currently in place on that window. The vertical zoom factor is used only for new, blank Waveview windows, since Scream! automatically chooses a suitable factor if it can.
Colour-coded Components : When this box is checked, Scream! will look for stream names ending Zn, Nn or En and automatically display them in the colours shown. To change the default colours, click on the boxes. Other streams are assigned a colour in rotation as they arrive. To define more specific colour defaults, you can use stream mapping (see below.)
Spectrogram : Alter this value to change the height of spectrograms displayed in Waveview windows, in pixels. When you click OK or Apply, newly-drawn spectrograms in all Waveview windows will use the new height. Pressing F5 will cause a Waveview window to be redrawn, as will resizing it, changing the zoom factor or using other buttons on the toolbar. Moving a window, or obscuring it and then revealing it, may or may not cause a redraw, depending on your operating system.
Units : Scream! can automatically scale new WaveView windows to physical acceleration units using sensitivity information you provide (see Section 2.8, page 19.) To enable this feature, first edit the calibration values for your digitizer, then select a suitable unit from the Displacement, Velocity, or Acceleration drop-down lists.
Once you have done this, streams from the digitizer will be scaled automatically. Other instruments will default to displaying in counts.
A simple linear scaling algorithm is used, which does not take into account the response profile of the instrument. For accelerometers, this is usually sufficient to be useful.
You can tell Scream! to look for streams with a particular Stream ID, and to display them in Waveview windows with their own colour and label. This is done from the setup window. As with all setup options, Scream! will remember any mappings you create, and restore them next time you run the program.
To create a new stream mapping:
From Scream!'s main window, choose File → Setup.... Switch to the Stream Mapping tab.
Check Use Stream Name Mapping. The pane will change to show the new options:
Click Add... and fill in the Stream ID you want to change, the new label and colour.
The label can be any length, but may not contain any of the characters
\ / : * ? " < > |
because these characters are not allowed in DOS or Windows filenames.
Click OK. In this example, new Waveview windows containing the DEMOZ2 stream will now automatically show it in the new colour, and with the label My 6TD vertical. The new label is also used in the main window, on printouts, and in the filenames of recorded data streams (if your format specifier includes the Stream ID.) Identifiers inside exported files will still use the original Stream ID.
Waveview windows which are already open will not change until they are refreshed (e.g. by resizing or zooming them, or by pressing F5.)
You can edit an existing mapping by double-clicking on its entry in the table, or by selecting it and clicking Edit.... To change the default colour only, click the colour panel under Col in the table.
To delete a stream name mapping, select it and click Remove.
Clicking Import... enables you to import a scream.ini file from another Scream! installation and extract the mappings from it. This is useful when you want to use a standard set of names and colours for several Scream! installations.