The phase relationship between channels should be maintained when processing multiple channel signals with Time-Scale Modification (TSM). This paper proposes a method and additional variant for maintaining the phase relationship between channels, and retaining the presence in the centre of the stereo signal as a result. The method involves pre- and postprocessing the file with the variant processing each frame for real-time suitability. Sum and difference transforms of the stereo signal are used for time-scale modification and results in a large improvement in stereo phase coherence as well as maintaining the stereo field. The proposed method produces a high quality stereo output and greatly improves quality over the independent channel processing method. It also allows for simple implementation, and can be implemented around existing TSM frameworks. The proposed method and variant are suitable for both frequency and time domain TSM methods. Availability: All source code, figures, and source audio files can be found at github.com/zygurt/TSM/.