This is a 4 RTL-SDR system. As calls come in, they are saved then played back. If another microphone queues up in that time, it will wait for the previous call to conclude, then it will play. It will catch 95% of all microphone key ups. Occasionally calls will be played out of order or twice, this is usually due to the recorder continuing to record and additional microphone key up. This is a direct audio output of www.harfordscanner.com.