OlinOvid wrote:Hi...What are the ballistics of PPM/BBC and PPM/EBU?
They are the same; only the scale is different. The specs are defined in IEC60268-10 iia (BBC) and iib (EBU).
10ms rise/2,8s fall to -24dB?
Integration time was 10ms. I think it was increased to 4ms in later versions of the spec. Off the top of my head the fall time is 20dB in 1.5 seconds.
And why is it that the reference is 7?
It isn't. The reference level on the BBC PPM is '4' which equates to 0dBu. On the EBU-scaled version, it's 0dBu/Test -- but both are at the point where the pointer is vertical.
Unless -18dBFS = 4 (BBC) and/or TEST (EBU). Then that's still a 18dB jump from 4 to 7 (3dB) - something can't be right.
Something isn't right... and I'm afraid it's your understanding... :-)
There's 4dB between each of the marks on a BBC PPM, so the level difference between PPM4 and PPM7 is 12dB. Like all analogue meters, there is headroom above the top of the display scale and the system's clipping level.
Normal programme peaks should be no higher than PPM6 (which is +8dBu on a steady tone), and PPM7 is achieved with a steady tone at +12dBu. But these readings are 'slugged' by the 10ms integration time, which means that brief signal transients will actually reach higher levels than the meter suggests, typically by about 4dB.
For that reason, the EBU decided that when digitising analogue signals controlled with a PPM, the alignment levels should be PPM4 = -18dBFS. So, although the mix should be restrained to PPM6 (allowing digital peaks to about -6dBFS) an occasional slip that displays as PPM7 (+12dBu) will actually have transients 4dB higher, and thus reach -2dBFS... which is as close to clipping as anyone would ever want to get! ;-)
What is the measurement window for the RMS meter? 300ms? 400ms (ITU-R MLk)? 600ms?
I'm not sure that RMS meters have a defined integration time. VU meters are 300ms, but I've seen RMS meters with integration times of 300ms to 1 second...
And why do you write "standard K-Meter modes, based on ITU 1770"
The K-meter -- as in Bob Katz' metering system -- has nothing whatever to do with ITU-R BS.1770. It is a simple RMS-based meter with an adjustable headroom margin, but a standard reference level which is aligned to a specific acoustic reference SPL. It is intended to aid mixing and mastering of material with different, genre-based, amounts of dynamic compression.
The K relates to its inventor, Bob Katz, and not the K-weighting EQ which forms a critical part of the ITU-R BS.1770 loudness metering standard.
...then it's basically a "K-weighted meter" (aka ITU-R BS.1770-0 or even 1), and not a default RMS realtime meter. Meaning, we have the same +3dB compensation/offset topic we had with dpMeter, no?
Sorry... I think my babel fish has gone to sleep... ;-)