Frames can be used to isolate disturbances difficult to spot by other means. When looking for an extraneous sound one usually tries to find the smallest segment of a soundfile where the disturbance is localized. One of the possible ways of doing it is to play a selected portion of the sound material gradually shrinking the search area by decreasing the size of the block (when using the Play block command) or increasing the time resolution (when using the Play window command). Unfortunately, as the auditioned fragment becomes shorter and shorter one finds it more and more difficult to judge whether or not it contains the disturbance - exactly as when attempting to analyze an image displayed for a very short period of time.
An alternative approach which we call 'framing', amounts to localizing the disturbance at the very beginning and at the very end of two longer, partially overlapping segments, respectively. If the disturbance is present in both fragments of a soundfile it must be contained in their common area and - bingo! - we've got it.
To set a frame:
1. Position the cursor so that the disturbance can be heard when the Play local command is used. Please note that the resolution of the frame-based search will increase when the local processing time is decreased. If necessary, use the Preferences dialog available from the Options menu to adjust the local processing time.
2. Choose the Set/Remove frame command from the Edit menu.
3. Move position of the upper play buffer in the Set/Remove frame dialog so that the disturbance remains audible and is located at the very end of the buffer.
4. Move position of the lower play buffer in the Set/Remove frame dialog so that the disturbance remains audible and is located at the very beginning of the buffer.
5. Click the Set button. The common (shaded) area of two buffers will be distinguished with a light blue frame displayed in the corresponding soundfile window. A similar mark (but in dark blue) will be also added to the overview strip.
Each time you open the Set/Remove frame dialog the common area of the upper and lower play buffers will be centered on the current cursor position. If so convenient you can adjust position of the cursor either inside the dialog (click anywhere inside the buffer display area) or outside the dialog (use any available way of changing the cursor position). In order to simultaneously shift both play buffers leftward or rightward change the cursor position and press the Center button - the center of the common area will be moved to the new cursor position. Finally, note that you can change the time resolution and/or the amplitude scale of all displayed plots without closing the Set/Remove frame dialog.
To remove a frame, invoke the Set/Remove frame dialog and press the Remove button. Note that since only one frame can be placed in a given soundfile window, when a new frame is added the previous one is automatically cancelled.
In order to position the upper/lower play buffers appropriately use the control buttons situated inside the Set/Remove frame dialog:
- moves the buffer leftward
- moves the buffer rightward
- plays contents of the buffer
- plays in a short succession the contents of the upper and lower buffer, respectively
- plays the contents of the common area of two buffers
NOTICE
Frames are not permanent, i.e. the frame is not restored when the corresponding soundfile window is closed and opened again. However, you can save the current position of all frames by saving a group of soundfiles (choose Save as from the Group menu).