|You should [wiki:/Help/AudioMapping/Calibration calibrate] the voice recorder's clock every so often, that is enter a reading to compensate for inaccuracy in your voice recorder's clock or audio sampling rate. This is most important with method 2, but will make working with the sound track easier for method 1. You can be certain that the clock in your GPS is highly accurate - GPS triangulation relies on extremely precise timing. However, audio recorders are often not so accurate, so you need to measure whether this is the case for your recorder and tell JOSM how much fast or slow it runs. An error of 5 seconds per hour would mean you could be 100m or more out after four hours surveying on a bike, and more in a car.