The Turning Point data reduction method [14] is basically an adaptive downsampling method developed
especially for ECGs. It reduces the sampling frequency of an ECG signal by a factor of two.
The method is based on the trends of the signal samples. Three input samples are processed at a time.
Let
x
(
n
) be the current sample at discrete-time instant
n
. Among the two consecutive input samples,
x
(
n
+ 1) and
x
(
n
+ 2), the one producing the highest slope (in magnitude) is retained and the other
sample is dropped. In this way the overall sampling rate is reduced to one-half of the original sampling
rate. no other coding is carried out. Therefore, the resulting CR is 2 to 1. A PRD of 5.3% is reported for
an ECG signal sampled at 200 Hz with 12 bit/sample resolution [14]. In practice the CR value actually
may be lower than 2 as the retained samples may not be equally spaced and some extra bits may be
needed for timing determination.