Universal notch filter
Systems, methods, and computer program product embodiments are disclosed for removing any fixed frequency interfering signal from an input signal without introducing artifacts that are not part of the original signal of interest. An embodiment operates by using a virtual buffer with a length that matches a length of one cycle of an interfering signal. The embodiment extracts the interfering signal into the virtual buffer. For a sample in the next cycle of the interfering signal that corresponds to a virtual memory location for the virtual buffer, the embodiment can update one or more physical memory locations of the virtual buffer that are in the vicinity of the virtual memory location. This use of virtual buffer can remove any interfering signal without creating the artifacts associated with conventional notch filters.
1. A universal notch filter comprising:
a memory configured to store a virtual buffer having virtual memory locations; and
at least one processor coupled to the memory and configured to:
access an input signal having an interfering signal;
determine a quiet period in the input signal;
update, during the quiet period, samples of the interfering signal in the virtual memory locations of the virtual buffer; and
subtract the samples from a single cycle of the interfering signal in the virtual buffer from the input signal to create a filtered signal, wherein the subtracting removes the interfering signal from the input signal.
2. The universal notch filter of claim 1 , wherein the at least one processor is further configured to:
calculate a non-quiet characteristic of the input signal; and
determine if the non-quiet characteristic is below a threshold value, thereby determining a presence of the quiet period.
3. The universal notch filter of claim 1 , wherein the updating by the at least one processor comprises:
averaging a sample of the input signal with a corresponding sample of the interfering signal in the virtual buffer to create an average sample; and
replacing the corresponding sample of the interfering signal in the virtual buffer with the average sample.
4. The universal notch filter of claim 3 , wherein the averaging comprises addition of a percentage of the input signal with a percentage of the corresponding sample of the interfering signal in the virtual buffer.
5. The universal notch filter of claim 1 , wherein the updating by the at least one processor comprises:
updating a physical memory location in the virtual buffer based on a sample of the interfering signal, wherein the sample of the interfering signal corresponds to a non-physically addressable memory location for the virtual buffer.
6. The universal notch filter of claim 1 , wherein a frequency of the interfering signal of the input signal is substantially constant.
7. The universal notch filter of claim 1 , wherein the processor is further configured to set a length of the virtual buffer to match a length of one cycle of a frequency of the interfering signal.
8. A non-transitory computer-readable medium having instructions stored thereon that, when executed by at least one computing device, cause the at least one computing device to perform operations comprising:
accessing an input signal having an interfering signal;
determining a quiet period in the input signal;
updating, during the quiet period, samples of the interfering signal in virtual memory locations of a virtual buffer; and
subtracting the samples from a single cycle of the interfering signal in the virtual buffer from the input signal to create a filtered signal, wherein the subtracting removes the interfering signal from the input signal.
9. The non-transitory computer-readable medium of claim 8 , wherein the determining comprises:
calculating a non-quiet characteristic of the input signal; and
determining the non-quiet characteristic is below a threshold value, thereby determining a presence of the quiet period.
10. The non-transitory computer-readable medium of claim 8 , wherein the updating comprises:
averaging a sample of the input signal with a corresponding sample of the interfering signal of the input signal in the virtual buffer to create an average sample; and
replacing the corresponding sample of the interfering signal in the virtual buffer with the average sample.
11. The non-transitory computer-readable medium of claim 10 , wherein the averaging comprises addition of a percentage of the input signal with a percentage of the corresponding sample of the interfering signal in the virtual buffer.
12. The non-transitory computer-readable medium of claim 8 , wherein the updating comprises:
updating a physical memory location in the virtual buffer based on a sample of the interfering signal, wherein the sample of the interfering signal corresponds to a non-physically addressable memory location for the virtual buffer.
13. The non-transitory computer-readable medium of claim 8 , wherein a frequency of the interfering signal of the input signal is substantially constant.
14. The non-transitory computer-readable medium of claim 8 , wherein the operations further comprise:
setting a length of the virtual buffer to match a length of one cycle of a frequency of the interfering signal.
15. A computer-implemented method for filtering an input signal to create a filtered signal, comprising:
accessing an input signal having an interfering signal;
determining a quiet period in the input signal;
updating, during the quiet period, samples of the interfering signal in virtual memory locations of a virtual buffer; and
subtracting the samples from a single cycle of the interfering signal in the virtual buffer from the input signal to create a filtered signal, wherein the subtracting removes the interfering signal from the input signal.
16. The computer-implemented method of claim 15 , further comprising:
calculating a non-quiet characteristic of the input signal; and
determining if the non-quiet characteristic is below a threshold value, thereby determining a presence of a quiet period.
17. The computer-implemented method of claim 15 , wherein the updating comprises:
averaging a sample of the input signal with a corresponding sample of the interfering signal in the virtual buffer to create an average sample; and
replacing the corresponding sample of the interfering signal in the virtual buffer with the average sample.
18. The computer-implemented method of claim 17 , wherein the averaging comprises addition of a percentage of the input signal with a percentage of the corresponding sample of the interfering signal in the virtual buffer.
19. The computer-implemented method of claim 15 , wherein the updating comprises:
updating a physical memory location in the virtual buffer based on a sample of the interfering signal, wherein the sample of the interfering signal corresponds to a non-physically addressable memory location for the virtual buffer.
20. The computer-implemented method of claim 15 , wherein a frequency of the interfering signal of the input signal is substantially constant.