DEVELOPMENT OF TEMPORAL LENSES WITH FIX AND VARIABLE MAGNIFICATION FOR SONIC REPRESENTATION OF CARDIAC SIGNALS
Introduction: Sonification is defined as representation by sound of a specific parameter of a signal (amplitude). Three distinct procedures can be applied: acoustic [A], with continuous variation of frequency, quasicontinuous [Q], with stepwise variation and sonic [S], with frequencies from musical scale, (not detailed here).
Tempolenses. For cardiac signals, the sonic display with the normal speed is too fast, hiding details. A dilation of time scale is similar to a temporal lens, or “tempolens”. Dilation factor is called magnification. We have used tempolenses with magnification 4x and compared the sounds with normal display (1x).
Fix and variable magnification. Tempolenses with fix magnification [f] increase all regions by the same factor. For emphasizing only regions with fast events (QRS),
tempolenses with variable magnification [v] have been built, with the ratio 2:1:0.5 for magnification in three regions of a period, in such a way that the overall magnification be 1x. Such lenses need complex algorithms, since the heart rate HR is not constant, and the regions must be defined starting from R peaks.
Signals. The lenses were tested on ECG clips of ten seconds (from Physiobank).
Software modules. The MATLAB R2011b platform was used for developing the processing modules, one main script, for choosing the signal and processing parameters and several functions for specific tasks: reading the signal, building the main matrix time-amplitude, both 1x and 4x, sound transition between two points (A or Q), R peak detector, sound frequency scale (linear/exponential) and graphic module.
Sonification parameters. The program yields graphs and sounds for all (eight) combinations of three sonification parameters: [A] vs. [Q], [f] vs. [v], [4x] vs. [1x].
Conclusion: The set of programs enables us to sonify any cardiac signal, ofering a convenient platform for studying the discriminant power of various procedures and to compare sonification with visualization.