The invention relates to a method and an apparatus for determining a spectrum of a sample comprising one or more constituent parts on the basis of a time the one or more constituent parts require to undergo a physical process or chemical process. The spectrum is determined by dividing the sample by a modulation unit into assays for which the physical process or chemical process is initiated successively, timed according to a modulation pattern which is a function composed of N consecutive modulation functions with N being 2 or larger, by measuring with a detector in N consecutive cycles a time when the constituent parts of the sample have completed the physical process or chemical process, wherein in succession of the cycles, each cycle is assigned to a consecutive one of the modulation functions within the modulation pattern, wherein each cycle is started with an offset in time as compared to a start of the modulation function it is assigned to, wherein for each cycle, the offset is different, wherein the detector provides a detector signal providing information on when what number of constituent parts have completed the physical process or chemical process and wherein the detector signal has a detection time resolution, wherein at least one of the offsets has an absolute value different from zero, different from the detection time resolution and different from multiples of the detection time resolution, and by calculating a correlation of the detector signal and the modulation pattern with a calculation unit.