19EURODESK SX4882 User Manual

◊With an LF cut at 100 Hz and a low shelf boost at 80 to 160 Hz, you have pretty much got a peak response rather than shelving at the bottom.

◊Look at the extraordinary width of the frequency sweep of the upper mid EQ -300 Hz all the way up. Set to maximum boost and play about with the frequency in real time. We bet you’ll get some stunning filter sweeps. Try it on drumloops – great for dance music!

◊You can cascade channel EQs by connecting the DIRECT OUT

(see section 7 “Connections”) of one channel into the LINE or TAPE INPUT of another. The first channel should first be un-routed to all buses, including L/R and aux sends. The second channel then becomes the “control” channel, routing to the buses. You now have a 23- channel mixer, but one channel has a 4-band (semi)-parametric plus 30 dB of shelving swing!

◊Remember EQ contouring can be done with CUT as well as BOOST. E.g.: cutting away the top and bottom, then pushing up the gain is equivalent to MID-RANGE BOOST! EQ is NOT a 1-way street!

◊Always re-set a channel’s input gain after altering the amount of EQ cut or boost applied (see 3.3).

10. Gain Optimization

PFL (Pre-Fader-Listening) is the way to set a desk level. Setting up the channel input gain is discussed in the essential section 13. Optimum master aux send levels will be dependent on the sensitivity of the FX device being driven,

but unity gain is a useful starting point. As the mix progresses, more and more channels are likely to be sending to effects via the aux buses, and it’s best to PFL all sends (aux, subgroup, MIX-B) just before setting up for the final mix.

Outboard reverbs etc. should all be made to work hard. There’s no point in having an 85 dB dynamic range if the input meter of your reverb is barely flickering.

On the other hand, digital distortion is not one of the nicer noises around. Fortunately you can SOLO the FX returns. Here you’ll have to rely on your ears to detect digital distortion, since different outboard processors calibrate their meters differently, and their dynamic range is not sufficient to allow, say, 15 dB of headroom (as is the case with DAT etc.). The PFL/SOLO meter, on the other hand, looks only at the desk’s analog aux input level, if you hear distortion, but the meter says you’re just hitting 0 dB, then it must be coming from the aux send amp or the FX unit. If PFL on the aux send reveals nothing amiss, turn down the input on the FX unit, and turn up the desk’s aux return.

◊99 times out of 100 distortion in the aux send > FX > aux return loop will come from the FX unit (FX GAIN TOO HIGH), and the same goes for a high noise level (FX GAIN TOO LOW).

◊Noisy FX (or synth) returns can be greatly improved by the addition of single-ended noise reduction between FX output and aux

(or channel) returns.

◊We found out that using analog single ended noise reduction can help warm the sound of certain digital reverbs which sound too cold/ metallic, and also give that “Echoplex” sound to digital delay decays.

◊Analog multitrack tape should be driven quite hard, since its dynamic range (without noise reduction) is likely to be 20 to 30 dB worse than other elements in the recording chain. Try to record bright. You can always mix back duller. Brightening up an off-tape signal will bring up the level of tape noise.

◊When mixing or recording, keep the channel FADER levels around or below 0 dB. If you do find the faders creeping up or down, apply a suitable offset over all channel faders, and try to control your bad habit in future!

11. Impedances and Tuning

Electronic inputs tend to have impedances measured in tens of kiloOhms. Outputs, on the other hand, are generally two or three orders of magnitude less. This is just as well, otherwise a signal at an output might find that the line of least resistance is the limit of the preceding unit.

In the patchbay section we recommended that you parallel the MAIN MIX output of the EURODESK SX4882 into all 2-track recording inputs. It would not do any harm to buffer each output from the primary one (i.e. that feeding into your most expensive DAT recorder or 1/2” mastering machine) with a 470 Ohm resistor. Cassette, DAT and reel to reel recorders’ input impedances should be similar, but just in case they aren’t, it is better to add a fraction of a dB of thermal noise to the inputs of the secondary recorders in the shape of a resistor, rather than having an unusually low impedance input grabbing most of the signal.

Another neat idea is to parallel the Monitor L/R output via a 47 kOhm resistor pair. Now you can safely connect e.g. a tuner to either extra hole, without shifting the stereo image (this would happen if a low impedance tuner input was connected directly across one side of the monitor output). Now, whenever you monitor an instrument’s input level with the PFL/SOLO function, you can check its tuning also. That should impress the customers. Especially those using old, unstable, but very desirable analog synths.

All output / input pairs normalised!

Fig. 11.1: Resistor-buffered parallel wiring for bay 8 (see section 8 “The patchfield”)

12. (Un)balanced Lines

Balanced inputs and outputs are offered on most audio connections on the EURODESK SX4882 (inserts and direct outs being the major exceptions).

Why? Though all audio cables (except speaker cables) have earthed screens, the shielding they afford from the electromagnetic garbage that permeates the atmosphere is never perfect. The balanced line is a simple but effective mechanism to overcome this problem. Instead of one insulated audio conductor, two, usually twisted together, are contained within a single screen. One conductor, wired to pin 2 of an XLR-type connector by international convention (after decades of total confusion!) carries a signal variously referred to as “hot” or “positive”. Pin 3 is wired to the “cold” or “negative” conductor.

What does this mean? Consider an unbalanced line. Now, that’s much easier to understand. You have one “hot” or “positive” core, and an earthed screen. The “hot” wire’s waveform, if looked at on an oscilloscope, would be directly correlated to the audio signal waveform. If you looked closely at the trace, you‘d see random noise along the X axis. What you probably wouldn’t see, however, is any superposition of 50, 100 Hz, etc. corresponding to mains hum interference, since these frequencies would be tangled up in the audio signal (to spot them visually you’d need to perform a FOURIER TRANSFORM). AC mains frequency and its overtones are picked up by any wire, and some will always leak through a cable screen. The question is, when does it become audible?

Well, all other things being equal, the amount of mains hum picked up by a cable is independent of the signal level. Speaker lines run 50 or more volts, enough to diminish the effect of mains radiation to vanishingly small even with no screen. (In fact, at these voltages another effect comes into play: capacitive resistance.

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