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N is just the number of calls whose measurements contributed to the other values. N will only be specificed when more than one call has contributed, and if N>1, it means that other values are averages over N calls. The exception are Next, Prev and TBC which will be averaged over the number of intervals between calls, which is always one less than N.
This is the Characteristic Frequency.
This is the Duration.
This is the Characteristic Slope in OPS.
This is the Initial Slope in OPS. It is the slope at the start of a call, and is particularly applicable where a call starts with a steep downsweep. In practice, this is measured by taking the first five dots in the call and measuring the slope between the first dot and each of the next 4 dots, then taking the largest slope value which comes out of this. The reason for this somewhat tortuous definition is that the positions of individual dots are subject to a small amount of noise (fluctuations in exact position) which have a large effect on slope values calculated using them. Note that the first dot needs to be in a good position. Typical bat calls start at low intensity and build up as the call progresses, which means that the first part of the call is often not well detected. In Anabat, a poorly detected signal can result in dots at unrealistically low frequencies, and any such intial dots should be excluded before the S1 values can have any meaning. Fortunately, such exclusion is usually easy because any filtering will generally remove such dots.
This is the lowest frequency in a pulse, and often at the end of a pulse. Because it is typically at the end of a downsweep of decreasing amplitude, the value measured can be highlyvariable, depending on how close the Bat is to the Bat Detector.
This measure is an attempt to put a value on the significance of the Knee in a call. The concept of the Knee is derived from the presence in many bat calls of a point at which the slope fairly abruptly changes from the initial, steep downsweep to the flattest part of the call, termed the Body. In reality, a gently curved call has no such point, nor does a truly linear call. The Body of the call is just that portion which has the lowest absolute slope (Sc), so it corresponds to the flattest part of the call. At the right hand end of the Body is the point with the Characteristic Frequency (Fc), and at the left hand end of the Body is the Knee. For a linear call, the Knee is at the start of a call, and the Body is the whole call. For a gently curved call, the Body doesn't really exist, and Fk might be equal to Fc.
In principle, the significance of the Knee depends on how abruptly the call slope changes from steep to flatter.
This measure is an attempt to put a value on the quality of the call being analysed. It is actually an average smoothness for the whole call. Smoothness is just the absolute value of the difference between the frequency of any point and the average of the frequencies of the points either side of it, divided by the frequency of that point. These values are summed over the whole call, and the result divided by the number of intervals in the call (number of dots minus 1). So:
for any 3 consecutive points with frequencies F1, F2 and F3,
Fav = ( F1+ F3 ) / 2
Q = abs [ ( F2 - Fav ) / Fav ]
Qual = sum of Q over all values in the call * 100 / (number of dots - 1 )
In effect, it is the average percentage deviation of the frequency of a dot from the average of the frequencies of the dots either side of it. High values are bad, low values are good.
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