An IEC Variant

The main problem with the IEC signal lies in its need for a noise source. Therefore, a new test signal is proposed that is equivalent to the IEC test signal. The noise source is replaced by 24 square waves of equal amplitude, all a factor 2 in frequency apart. In the frequency range from 10 Hz up to 28 kHz, this simulates pink noise, since the energy per octave is constant. This semi pink noise is filtered to get the IEC frequency characteristics. An additional advantage is that the signal, which had only 24 possible amplitude values, now becomes continuous. Only 100 ms of simulation with this IEC variant suffice, since frequency components below 10 Hz are not present. The square waves are easy to define in a circuit simulator, which will speed up simulations. Also, such a signal can easily be generated in hardware with binary counters or with IC’s that are used as tone generators in electronic organs. To see if this IEC variant is indeed equivalent, the dissipation curves for the three amplifier classes were measured, this time for the IEC signal and its variant. The results in Picture 1 show that the dissipations are almost the same at low output powers. At high output powers, the results differ more. Since heat sink temperature measurements on more than one high power music fragment are not available, it remains unclear if this error is the same for all music fragments at that output power. However, the differences are rather small and only occur when the signal is heavily clipping. At lower, more usual output powers, the IEC variant gives good results.

Picture 1: Measured dissipation of three amplifier classes for the IEC signal and the IEC variant