Audio Engineering

(Barry) #1
Recording Consoles 771

27.4 Digital Line-Up .....................................................................................................


The question of how to relate 0 VU and PPM 4 to a digital maximum level of 0 dBFS
(for 0 dB relative to full scale) has been the topic of hot debate. Fortunately, the situation
has crystallized over the last few years to the extent that it is now possible to describe
the situation on the basis of widespread implementation in the United States and with
European broadcasters. Essentially,


0 V U   4 dBu   20 dBFS (SMPTE RP155)


PPM4  0 dBu   18 dBFS (EBU R64-1992)


Sadly, these recommendations are not consistent. And while the EBU recommendation
seems a little pessimistic in allowing extra 4-dB headroom above their own worst-case
scenario, the SMPTE suggestion looks positively gloomy in allowing 20 dB above the
alignment level. Although this probably refl ects the widespread, although technically
incorrect, methodology, when monitoring with VUs, of setting levels so that peaks often
drive the meter well into the red section.


27.5 Sound Mixer Architecture and Circuit Blocks


The largest, most expensive piece of capital electronic equipment in any professional
studio is the main studio mixer. So much so that in publicity shots of a recording studio
this component is always seen to dominate the proceedings! Perhaps that’s why there
seem to be so many terms for it: mixer, mixing desk, or just desk, audio console, console,
and simply “ the board, ” to name but a few. To many people outside of the recording
industry, the audio mixer represents the very essence of sound recording. This is partially
correct, for it is at the console that many of the important artistic decisions that go toward
mixing a live band or a record are made. However, in engineering terms, this impression
is misleading. The audio console is a complicated piece of equipment but, in its electronic
essence, its duties are relatively simple. In other words, the designer of an audio mixer
is more concerned with the optimization of relatively simple circuits, which may then be
repeated many, many times, than he/she is with the design of clever or imaginative signal
processing. But before we investigate the individual circuit elements of an audio mixer,

Free download pdf