Rupert-neve Portico 5017 - Mobile DI/Pre/Comp User Manual download pdf (Page 4)

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In the early 1960’s when the “Pop” music scene was exploding and sound levels in the Studio became

very high, there was concern that the head ampliers in Condenser microphones would overload if the

Console input impedance was too low. In the early days of Consoles I was asked to provide higher input

impedance than the normal 1,000 ohms. This of course, resulted in less “step-up” in the Console input

transformer and there were then fears that we would lose out at the other end of the scale; Noise. The

fact that microphones were less heavily loaded allowed an increased microphone signal. The reduced

loading also resulted in less deviation of frequency response due to variation of microphone impedance

and consequently less distortion at high levels.

The Portico 5017 microphone amplier provides an input impedance of 10,000 ohms which means that

variations in microphone source impedance with frequency, have only a very small effect on the sonic

quality. This high input impedance has minimal effect on microphone output and loading with the result

that microphone distortion is very low adding up to a noticeable improvement in “transparency”.

A NOTE ON DISTORTION

The human hearing system is a remarkably complex mechanism and we seem to be learning more

details about its workings all the time. For example, Oohashi demonstrated that arbitrarily ltering out

ultrasonic information that is generally considered above our hearing range had a measurable effect on

listener’s electroencephalo-grams. Kunchur describes several demonstrations that have shown that our

hearing is capable of approximately twice the timing resolution than a limit of 20 kHz might imply

(F=1/T or T=1/F). His peer reviewed papers demonstrated that we can hear timing resolution at

approximately with 5 microsecond resolution (20 kHz implies a 9 microsecond temporal resolution,

while a CD at 44.1k sample rate has a best-case temporal resolution of 23 microseconds).

It is also well understood that we can perceive steady tones even when buried under 20 to 30 dB of

noise. And we know that most gain stages exhibit rising distortion at higher frequencies, including

more IM distortion. One common IM test is to mix 19 kHz and 20 kHz sine waves, send them through

a device and then measure how much 1 kHz is generated (20-19=1). All this hints at the importance

of maintaining a sufcient bandwidth with minimal phase shift, while at the same time minimizing

high frequency artifacts and distortions. All of the above and our experience listening and designing

suggest that there are many subtle aspects to hearing that are beyond the realm of simple traditional

measurement characterizations.

The way in which an analog amplier handles very small signals is as important as the way it behaves

at high levels. For low distortion, an analog amplier must have a linear transfer characteristic, in other

words, the output signal must be an exact replica of the input signal, differing only in magnitude. The

magnitude can be controlled by a gain control or fader (consisting of a high quality variable resistor

that, by denition, has a linear transfer characteristic.) A dynamics controller - i.e. a compressor,

limiter or expander - is a gain control that can adjust gain of the amplier very rapidly in response to

the uctuating audio signal, ideally without introducing signicant distortion, i.e. it must have a linear

transfer characteristic. But, by denition, rapidly changing gain means that a signal “starting out” to be

linear and, therefore without distortion, gets changed on the way to produce a different amplitude.

Inevitably our data bank of “natural” sound is built up on the basis of our personal experience and

this must surely emphasize the importance of listening to “natural” sound, and high quality musical

instruments within acoustic environments that is subjectively pleasing so as to develop keen awareness

that will contribute to a reliable data bank. Humans who have not experienced enough “natural”

sound may well have a awed data bank! Quality recording equipment should be capable of retaining

“natural” sound and this is indeed the traditional measuring stick. And “creative” musical equipment

should provide the tools to manipulate the sound to enhance the emotional appeal of the music without

destroying it. Memory and knowledge of real acoustic and musical events may be the biggest tool and

advantage any recording engineer may possess.

One needs to be very careful when one hears traces of distortion prior to recording because some avors

of distortion that might seem acceptable (or even stylish) initially, may later prove to cause irreparable

damage to parts of the sound (for example, “warm lows” but “harsh sibilance”) or in louder or quieter

sections of the recording. Experience shows that mic preamps and basic console routing paths should

offer supreme delity otherwise the engineer has little control or choice of recorded “color” and little

recourse to undo after the fact. Devices or circuits that can easily be bypassed are usually better choices

when “color” is a consideration and this particularly is an area where one might consider comparing

several such devices. Beware that usually deviations from linearity carry at least as much long-term

penalty as initial appeal, and that one should always be listening critically when recording and generally

“playing it safe” when introducing effects that cannot be removed.

1. Tsutomu Oohashi, Emi Nishina, Norie Kawai, Yoshitaka Fuwamoto, and Hishi Imai. National

Institute of Multimedia Education, Tokyo. “High Frequency Sound Above the Audible Range,Affects Brain Electric Activity and

Sound Perception” Paper read at 91st. Convention of the A.E.S.October 1991. Section 7. (1), Conclusion.

2. Miland Kunchur,Depart of Physics and Astronomy, University of South Carolina. “Temporal resolution of hearing probed

by bandwidth restriction”, M. N. Kunchur, Acta Acustica united with Acustica 94, 594–603 (2008) (http://www.physics.

sc.edu/kunchur/Acoustics-papers.htm)

3. Miland Kunchur,Depart of Physics and Astronomy, University of South Carolina.Probing the temporal resolution and

bandwidth of human hearing , M. N. Kunchur, Proc. of Meetings on Acoustics (POMA) 2, 050006 (2008)

5017 USAGE NOTES

The 5017’s small size and feature set allows it to be used in many different ways, in both studio and live

environments. The diagrams on the following pages show how to use the 5017 as a single channel or

dual channel module. Here are some creative things to try:

For vocals, take two mics, your favorite condenser plugged into the Mic Input, and a SM57 or SM58 set

up 6 inches closer to the vocalist and plugged into another mic pre, then into the 5017 Inst Input. Adjust

Vari-Phase to taste, and maybe add some light compression from the 5017 followed by your usual vocal

compressor, which may behave even nicer because of that touch of “pre-compression” from the 5017.

For synth(or another instrument), set the signal chain as seen for single channel use(Page 8), but

place the mic a little further than normal from the amp, or pointed away from the amp to incorporate

more room reections. With the mic even further away, we might suggest using the Mic Pre Output

sent to a separate track and the Blend control set to INST so you end up with separate “dry” and a

“room” tracks(See Page 9 setup). In the latter example, the Phase Sweep may be rather subtle and the

compressor can be set to operate on either the DI (dry) or mic (room) signal depending on the internal

jumper. With the compressor set to the mic path, you may nd this accentuates the room nicely, and

if you are changing jumpers, you might want to audition the “slow” compressor jumper setting while

you are there. This may work also work well for “re-amping” some tracks already recorded on the DAW,

especially given the Phase Sweep and Compressor in the 5017.

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Rupert-neve Portico 5017 - Mobile DI/Pre/Comp User Manual Page 4

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