An asynchronous AC measurement system comprising: a. an isolated current channel converter (103A - 103D, 203A- 203D) configured to transform a current applied to the input by a power signal to a current within a predetermined range and digitizes said current, wherein said isolated current channel converter comprises a two stage current transformer configured to convert the secondary current generated in the first stage of the two stage transformer to a voltage; to convert a compensating secondary current generated in the second stage of the two stage transformer to a compensating voltage; and to add the voltages after conversion; b. an isolated voltage channel converter (104A - 104D, 204A - 204D) configured to transform a voltage applied to the input by the power signal to a voltage within a predetermined range and digitizes said voltage; and c. a digital analyzer (107, 207, 300) comprising at least a microprocessor configured to process said digital representations of the voltage and current of the input signal to determine at least one of a parameter of the input signal and a power quality parameter of the input signal, wherein said digital representations of the voltage and current are generated by digitally sampling at a sampling frequency that is independent of the signal being analysed, wherein processing said digital representations of at least one of the voltage and current of the input signal comprises: splitting said digital representation into at least two sub-streams of a plurality of sub-streams, each sub-stream comprising a portion of the digital representation established in dependence upon a predetermined threshold; processing each sub-stream of the plurality of sub-streams independently to establish a sub-stream output; and processing the plurality of sub-stream outputs to generate an output. a. an isolated current channel converter (103A - 103D, 203A- 203D) configured to transform a current applied to the input by a power signal to a current within a predetermined range and digitizes said current, wherein said isolated current channel converter comprises a two stage current transformer configured to convert the secondary current generated in the first stage of the two stage transformer to a voltage; to convert a compensating secondary current generated in the second stage of the two stage transformer to a compensating voltage; and to add the voltages after conversion; b. an isolated voltage channel converter (104A - 104D, 204A - 204D) configured to transform a voltage applied to the input by the power signal to a voltage within a predetermined range and digitizes said voltage; and c. a digital analyzer (107, 207, 300) comprising at least a microprocessor configured to process said digital representations of the voltage and current of the input signal to determine at least one of a parameter of the input signal and a power quality parameter of the input signal, wherein said digital representations of the voltage and current are generated by digitally sampling at a sampling frequency that is independent of the signal being analysed, wherein processing said digital representations of at least one of the voltage and current of the input signal comprises: splitting said digital representation into at least two sub-streams of a plurality of sub-streams, each sub-stream comprising a portion of the digital representation established in dependence upon a predetermined threshold; processing each sub-stream of the plurality of sub-streams independently to establish a sub-stream output; and processing the plurality of sub-stream outputs to generate an output. splitting said digital representation into at least two sub-streams of a plurality of sub-streams, each sub-stream comprising a portion of the digital representation established in dependence upon a predetermined threshold; processing each sub-stream of the plurality of sub-streams independently to establish a sub-stream output; and processing the plurality of sub-stream outputs to generate an output.