[Iain Churches[_2_]]

Some time ago, we touched on the topic of
analogue metering, VU and PPM, and I mentioned the
PPM used at Decca UK when I was there.

I have now been able to get my hands on one of these
(I wish it had been a pair:-)

Pic at:

http://www.kolumbus.fi/iain.churches...tTurnerPPM.jpg

The Decca PPM has a range of 46dB (-30 to +16dBm)
and was designated type 703 and made by perhaps the finest
British maker, Ernest Turner. As you can see from the pic,
this one does not have a red sector at all, as on the VU, (type
702) but simply a red line at +8dBm. (2V into 600 Ohms)

The Ernest Turner VU (type 702) can be seen at:

http://www.kolumbus.fi/iain.churches...tTurner702.jpg


The rise time of the PPM is 10mS (thirty times faster than the VU)
and the fall back time is (IIRC) 2Sec.


There was a later version that had a faster rise time, with
the red line at +12dBm. I can only recall ever seeing one pair
of these (perhaps they were experimental) in a pop remix
suite.

It is totally different to (and not to be confused with)
the BBC PPM which had a much smaller dynamic range
on the scale which was caibrated from 0-8. Only seven
divisions, 1-7 were labelled, zero and 8 being unmarked.
Peak level was +6.

Hence the corruption of the BBC motto:
"Nation shall speak unto Nation" into "Nation shall peak
six unto Nation" :-)

The BBC PPM has a distinctive black face with while
lettering. Some are marked "Peak Level" some have
no legend at all. The design dates back to the mid 30s
(about the same time as the VU came into use in the US)
and was also known as the Smith meter after its designer.
Early versions had a right hand electrical zero.

There was also a stereo meter with two movements
and two needles one one scale. The needles were
red (left) and green (right)

In addition, the paper: Implementing Methods for Equal Loudness
in Radio Broadcasting, by Matti Zemack of Swedish Radio
may be of interest.

http://www.speech.kth.se/prod/public...files/3098.pdf


Best regards

Iain