Click here to purchase the entire book in PDF format. Scale The good thing about VU Meters is that they show you the average level of the signal - so they're great for recording to analog tape or for mastering purposes where you want to know the overall general level of the signal. However, they're very bad at telling you the peak level of the signal - in fact, the higher the crest factor, the worse they are at telling you what's going on. As we've already seen, there are many applications where we need to know exactly what the peak level of the signal is. Once upon a time, the only place where this was necessary was in broadcasting - because if you overload a transmitter, bad things happen. So, the people in the broadcasting world didn't have much use for the VU Meter - they needed to see the peak of the program material, so the Peak Program Meter or PPM was developed in Europe around the same time as the VU Meter was in development in the US. A PPM is substantially different from a VU Meter in many respects. These days it has many different incarnations - particularly in its scale, but the traditional one that most people think of is the UK PPM (also known as the BBC PPM). We'll start there. The UK PPM looks very different from a VU Meter - it has no decibel markings on it - just numbered indications from ``Mark 0'' up to ``Mark 7.'' In fact, the PPM is divided in decibels, they just aren't marked there - generally, there are 4 decibels between adjacent marks - so from Mark 2 to Mark 3 is an increase of 4 dB. There are two exceptions to this rule - there are 6 decibels between Marks 0 and 1 (but note that Mark 0 is not marked). In addition, there are 2 decibels between Mark 7 and Mark 8 (which is also not marked). Because we're thinking now in terms of the peak signal level, the nominal level is less important than the maximum, however, PPM's are calibrated so that Mark 4 corresponds to 0 dBu. Therefore if the PPM at the output stage on a mixing console read Mark 5 for a 1 kHz sine wave, then the output level is $1.228 V_{RMS}$ between pins 2 and 3 (because Mark 5 is 4 dB higher than Mark 4, making it +4 dBu). Figure 10.16: A photograph of a typical UK (or BBC) PPM on the output module of a Sony/MCI mixing console. Figure 10.17: An RTW UK PPM variation. There are a number of other PPM Scales available to the buying public. In addition to the UK PPM, there's the EBU PPM, the DIN PPM and the Nordic PPM. Each of these has a different scale as is shown in Table 10.1 and the corresponding Figure 10.18. Figure 10.18: Various scales of analog level meters for professional recording equipment. Add 4 dB to the corresponding signal levels for professional broadcasting equipment. Figure 10.19: INSERT CAPTION Figure 10.20: An RTW Nordic PPM.