Digital filter

1. A digital filter comprising:

a local frequency state detector configured to indicate a predetermined local frequency state in a sequence of data values, the local frequency state detector including a rate-of-change calculator configured to calculate a change of value between values of the sequence and a rate-of-change evaluator configured to evaluate the change of value calculated by the rate-of-change calculator;

a regional frequency state detector configured to detect a predetermined condition in a region of the sequence, based on a plurality of local frequency state indications determined by the rate-of-change evaluation, and to output a select signal based on the detection;

a compensator configured to output a compensated value of a value of the sequence; and

a selector configured to output one of the value and the compensated value, based on the select signal.

2. The digital filter according to claim 1 , wherein the compensator includes a saturating adder.

3. The digital filter according to claim 1 , wherein the rate-of-change calculator is configured to calculate a change of value between consecutive values of the sequence.

4. The digital filter according to claim 1 , wherein the regional frequency state detector includes a condition detector configured to detect a high-frequency region of a predetermined length.

5. A method of signal processing, said method comprising:

digitizing an analog signal having amplitude information;

detecting in the digitized signal an amplitude transition having a magnitude at least equal to a predetermined threshold value using a rate-of-change calculator configured to calculate a change of value between values of a sequence;

evaluating the change of value calculated by the rate-of-change calculator; and

in response to the evaluating, increasing the magnitude of the amplitude transition with respect to other amplitude transitions in the digitized signal.

6. A method of signal processing, said method comprising:

digitizing an analog signal having amplitude information;

calculating a rate-of-change value between values of a sequence;

evaluating the rate-of-change value calculated;

storing a plurality of the rate-of-change evaluations;

detecting a high- frequency region of the digitized signal based on the plurality of the rate-of-change evaluations; and

in response to said detecting, increasing a high-frequency content of the digitized signal in at least a portion of the high-frequency region.

7. The method of signal processing according to claim 6 , wherein said detecting a high-frequency region of the digitized signal includes detecting a predetermined plurality of local frequency states within the region.

8. The method of signal processing according to claim 6 , wherein said increasing a high-frequency content of the digitized signal in at least a portion of the high-frequency region includes determining that a magnitude of a value of the digitized signal does not exceed a predetermined threshold.

9. A method of signal processing, said method comprising:

detecting the presence of a first particular frequency state at a plurality of locations of a sequence of digital values using a rate-of-change calculator configured to calculate a change of value between values of the sequence;

evaluating the change of value calculated by the rate-of-change calculator;

based on the evaluation of the change of value, determining whether a condition exists with respect to a region of the sequence including the plurality of locations;

producing a compensated value based on a value of the sequence; and

according to said determining, selecting one among the compensated value and a value on which the compensated value is based.