The NTP type 477-400 are a Digital Peak Level Meter. The input connects directly to the Serial Digital Audio Signal, as described in the EBU 3250, IEC 958 and AES3 standards. This instrument combines the scale of the „absolute“ type, meaning that the scale maximum (marked „0“) corresponds to maximum digital code level, with the scale for analog PPM, which adheres to IEC 268-10 standards. In this way, it enables a Sound Engineer, working in a mixed analog and digital environment, to make direct comparison between audio signals.