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Nyt kun tuli puheeksi tiskien soundin erot ja mistä ne johtuvat, niin muistin erään keskustelun toiselta puolelta nettiä. Siellä A&H:n mikserisuunnittelija (ainakin jossain vaiheessa taisi olla ihan pamppuna siellä) Carey Davies kertoili vähän omia kommenttejaan tuohon liittyen ja kysyin sitten lupaa pasteta hänen tekstinsä tänne. Tässä se nyt tulee, valitettavasti vain lontooksi. Lupaili myös vastailla ihmisten kommentteihin, jos sellaisia tulee. Voin vaikka odotella muutaman päivän ja välittää ne sitten kootusti, jos tarvetta ilmenee, niin ei turhaan pommiteta hänen postilaatikkoaan miljoonilla maileilla.
 
Olkaatten hyvät, ehkä tuo vastaa jonkun ihmisen ihmettelyihin. Toivottavasti ainakin. :)
 
Olli
 
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Well, you've got me started... There is a lot more to this than the
'math'. :-)
 
To some it is very subjective, to others more to do with how good the
lab figures are. Some relate it to the mic pre, others the
responsiveness of the EQ. Some are influenced by the brand, and may be
surprised when taking a blind listening test. Others talk about the cost
of the components. For some what sounds 'good' can be a colouration of
the original material adding 'warmth' or 'depth', while for others it is
about accuracy and clarity. Some judge by A-B comparisons using CD,
others using live sources, and some remember how different systems
sounded during different shows.
 
For me, how a console sounds has been a big part of my lifes work with
Allen & Heath, both as a console designer and user. Whilst not endowed
with the biggest budget or unlimited resources to explore this, I have
seen and heard many developments over the years. And while I accept that
personal taste and perception remain a big factor, I believe there are
many aspects to what makes any equipment sound good.
 
Technically it is a lot more than just one part of the design. It is a
combination of the many elements that combine to process the signal from
input to output.
 
The preamp is of course very important as it is the gateway to the
console from a wide variety of often unpredictable and imperfect
sources. A well buffered low impedance CD may sound clean through this
stage, but a mic with its higher and more variable impedance, and prone
to instability and interference over long cable runs may produce a less
than perfect sound. For example a preamp that becomes unstable and
oscillates at a very high and therefore inaudible frequency may still
work but with its output coloured by increased noise and modulation.
Depending on the input stage design, a higher impedance mic may suffer
variable attenuation at high or low end frequencies. How a preamp clips
is an important factor too. Most of these issues can be measured and
seen using lab equipment with the results reflected in noise, frequency
response and distortion figures.
 
People talk about the 'headroom' of the preamp. Often, this is
misinterpreted from the feel of the gain pot where turning the control
more than you would on another console gives the perception that it has
less headroom. Of course this is not necessarily the case. It is simply
down to the law of the pot used. There are two real aspects to preamp
headroom, how much level it puts out before it clips, and how much level
you can put in before it clips. The latter is more important as it
determines how much control you have when working with increasingly hot
signals such as kick and CD. The topology of our more recent A&H designs
allows signals as high as +30 or +34dBu at the XLR input. You would not
expect to average anywhere near those levels, but you may well need the
dynamic headroom it provides...
 
A similar issue is the 'responsiveness' of the EQ. Once again many
engineers interpret the law of the cut/boost control as a reflection of
quality of the circuit. Two consoles with different pot law may be just
as good. The different pot positions represent the same amount of cut or
boost. Maximum position represents the same capability. Making our A&H
EQ more responsive on recent consoles has focused mostly on changing the
law of these controls.
 
Another aspect of how the EQ 'sounds' relates to the Q or slope of the
frequency response, and the extents of the frequency ranges. On lower
end consoles without Q control it is a case of striking a compromise
between high Q (width) for feedback/resonance notching, or low Q for
making wider adjustments to add warmth, cut harshness etc. A mid that
sweeps its centre frequency down to a low 35Hz may seem strange or
excessive, but it does drastically improve the control you have over the
low end beyond what you can do with just the LF shelving stage alone.
 
While you can judge how a console sounds with its EQ flat, or believe
that you do not need to do much EQ'ing because of the more responsive
law of the control, what matters most is how it sounds once you have
adjusted for the mic used, its position, the source, affect of acoustic
reflections, resonances and all the other real world issues that
challenge the live sound environment.
 
A very underrated part of the console design is the bus head amp, the
stage that mixes all the channel signals together. This has been a big
part the focus of our design team. A good design ensures low residual
mix noise and high headroom to deal with the dynamics of combining so
many channel sources together. Aspects such as how fast the circuit
responds, combined bus impedance, bus interference rejection, and more
are considered. Like the mic preamp, the mix amp front end is critical
to the resulting performance and sound. The new low noise discrete front
end of the recent GL consoles is a result of extensive work in this
area.
 
Probably the most critical aspects of the design which affects overall
console performance are the grounding, signal shielding and power rail
distribution. The very lowest impedance ground and power rail paths
ensure a 'tight' signal. A thick copper ground bus strip placed across
all the channel circuit cards does wonders in ensuring proper ground
integrity. XLR pin 1 and TRS jack shield metal to metal bonding to
chassis ground avoids ground loop problems and helps meets the stringent
requirements of the EMC (electromagnetic compatibility) standards.
Effective shielding of sensitive signals, particularly within the EQ and
mix amps, and careful track routing during pcb layout reduces crosstalk
and interaction between signals. Even tiny amounts of crosstalk within a
circuit may introduce an interaction that affects or degrades the way
the console sounds.
 
Component choice is obviously important. However, it is not always a
case of 'the more expensive, the better it is'. Of course, compromises
should not be taken. With most of our designs I prefer to sacrifice such
things as fancy trims and decals in favour of signal integrity and
proper interface connectivity. Both lab and subjective listening tests
are critical to component choice and circuit design. It is an exhaustive
process as the resulting sound is only as good as the weakest component
in the signal path...
 
And then there is the getting out there and using the console for
real...
 
I could go on a lot more but it's time to get back to my 'Black Magic of
Designing Consoles' book! :-)
Have a good day,
Carey
 
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