A method of detecting a touch event on an acoustic fingerprint based touch system, comprising: digitizing (231, 232, 502, 504, 506) first signals from at least a first sensor to form a first set of digitized signals and second signals from at least a second sensor to form a second set of digitized signals, wherein the at least first and second sensors (106, 108, 110, 112) are associated with a touch panel; performing (233, 234, 508, 509, 510) a frequency transform upon the first set of digitized signals and the second set of digitized signals to form respectively first and second frequency transform data sets of frequency components; constructing (241, 242, 518) for a touch a first live fingerprint indicating a touch location and a second live fingerprint indicating a touch location; and identifying the location of the touch based on the first and second live fingerprints, wherein the identifying comprises comparing (243, 244, 524, 525, 526) each of the at least first and second live fingerprints to a plurality of template fingerprints (140-144, 174-178) wherein each of the template fingerprints is associated with coordinates on the touch panel, wherein the identifying further comprises identifying (243, 244, 524, 525, 526) a best matching template fingerprint associated with each of the at least first and second live fingerprints based on the comparison to provide the location of the touch, characterised in that the first live fingerprint is constructed based on a magnitude ratio comprising a ratio between the amplitude magnitudes of the first frequency transform data set and the second frequency transform data set, and the second live fingerprint is constructed based on a phase difference comprising a difference between phase information associated with the first frequency transform data set and second frequency transform data set, such that each of the first and second live fingerprints is gauge-invariant. digitizing (231, 232, 502, 504, 506) first signals from at least a first sensor to form a first set of digitized signals and second signals from at least a second sensor to form a second set of digitized signals, wherein the at least first and second sensors (106, 108, 110, 112) are associated with a touch panel; performing (233, 234, 508, 509, 510) a frequency transform upon the first set of digitized signals and the second set of digitized signals to form respectively first and second frequency transform data sets of frequency components; constructing (241, 242, 518) for a touch a first live fingerprint indicating a touch location and a second live fingerprint indicating a touch location; and identifying the location of the touch based on the first and second live fingerprints, wherein the identifying comprises comparing (243, 244, 524, 525, 526) each of the at least first and second live fingerprints to a plurality of template fingerprints (140-144, 174-178) wherein each of the template fingerprints is associated with coordinates on the touch panel, wherein the identifying further comprises identifying (243, 244, 524, 525, 526) a best matching template fingerprint associated with each of the at least first and second live fingerprints based on the comparison to provide the location of the touch, characterised in that the first live fingerprint is constructed based on a magnitude ratio comprising a ratio between the amplitude magnitudes of the first frequency transform data set and the second frequency transform data set, and the second live fingerprint is constructed based on a phase difference comprising a difference between phase information associated with the first frequency transform data set and second frequency transform data set, such that each of the first and second live fingerprints is gauge-invariant.