Efficient median filter and method therefor

A engine combustion performance system comprising:

• a data acquisition system for capturing data samples indicative of engine combustion performance in terms of acceleration;
• a memory circuit for storing N time ordered data samples from the data samples captured by the data acquisition system;
• a first grading circuit for determining a first metric and a second metric for each data sample of the N time ordered data samples, said first metric indicative of a quantity of data samples of the N time ordered data samples, exclusive of said each data sample, that have a magnitude less than a magnitude of said each data sample, and said second metric indicative of a quantity of data samples of the N time ordered data samples, exclusive of said each data sample, that have a magnitude less than or equal to the magnitude of said each data sample;
• and
• a second grading circuit for determining a data sample of the N time ordered data samples having a magnitude median within the N time ordered data samples by identifying which data sample of the N time ordered data samples has a first metric with a magnitude less than or equal to (N-1)/2, and a second metric with a magnitude greater than or equal to (N-1)/2.

In an efficient median filter having a first and second grading circuit, a method of determining a median value of a continuous stream of data samples comprising the steps of:

• capturing N time ordered data samples into a memory circuit from the continuous stream of data;
• finding, for each, data sample of the N time ordered data samples, in the memory circuit, a first metric by said first grading circuit and a second metric by said second grading circuit, wherein the first metric is a measure of a quantity of data samples of the N time ordered data samples, exclusive of said each data sample, that have a magnitude less than a magnitude of said each data sample, and wherein the second metric is a measure of a quantity of data samples of the N time ordered data samples, exclusive of said each data sample, that have a magnitude less than or equal to the magnitude of said each data sample;
• and
• determining a data sample of the N time ordered data samples, in the memory circuit, the data sample having a magnitude median within the N time ordered data samples by identifying the data sample of the N time ordered data samples having a first metric with a magnitude less than or equal to (N-1)/2, and a second metric with a magnitude greater than or equal to (N-1)/2.