Implement LUFS opcode

[kunstmusik]

As mentioned on the Csound list, an opcode for measuring LUFS (momentery, short-term, and integrated) would be great in Csound. Some notes:

• Spec in https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-2-201103-S!!PDF-E.pdf
• Fons' ebumeter for reference (https://kokkinizita.linuxaudio.org/linuxaudio/ebumeter-doc/quickguide.html)

[gleb812]

ITU-R BS.1170-2 standardizes mono, stereo or 5.1 format. It doesn't deal with 8 channel system typical for computer music. Should we go for up two channels only so far?

[kunstmusik]

I think up to two channels would be great to start and ignoring 5.1 is fine. If someone really wants it we can revisit.

Looking through all of this I forgot that getting dB True Peak would be useful too as an opcode. Perhaps something we can look at after this.