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Sound Advice

More readers' queries are answered by the expert teaching staff of London's Gateway School of Recording & Music Technology.


A regular column where members of the teaching staff of the Gateway School of Recording & Music Technology answer your questions.

ALL MIXED UP?


I have recently purchased a new mixer and am confused about when I should be using my effects sends or insert points. Can you clarify this for me?
Stanley Barnes
Dyfed

Dave Ward, who teaches the recording courses at Gateway, replies:

In answering this question it is useful first of all to define two different types of outboard equipment. These we will call signal processors as opposed to effects.

A signal processor is a device like a graphic equaliser, compressor or a noise gate, which processes or alters a signal flowing through it and generally doesn't have any mixing facility to vary the balance of a clean signal with a processed signal. For instance, if we were to compress the dynamics of an acoustic guitar we would be acting only on the acoustic guitar and the processed signal would come from the output of the compressor. (This is a very 'grey' area but we will continue.)

If we are working only on one instrument or signal it would be sensible to make our signal processor part of the channel in which the signal is appearing. The insert points on a mixer are provided for this very purpose, allowing a processor to be inserted in the signal path of an input channel, a group output, or indeed across the final stereo mix outputs of the mixer.

An effect, rather than a processor, will impose an effects treatment on the signal which we will probably want to mix with the 'dry', untreated signal itself. For instance, this effect could be some form of delay or reverb, chorus, flanging etc.

Sometimes it might be appropriate to connect an effects unit across the insert points of a mixer channel if we only wanted to effect whatever sound was in that particular channel. In this case we would need some form of mixing control on the outboard effects device itself to be able to mix the treated and untreated signals together.

When using an insert point for use by effects, you don't have the facility to pan the effected signal to a different position from the original and thereby create a stereo feel to the sound. Insert points are mono! Even though they typically use a stereo jack to send the signal out to the effects unit and return it to the mixer channel.

However, with many effects units - particularly reverb - we will wish to send a 'mix' or combination of several signals to the unit to be effected. We might, for instance, send a little snare drum, some vocals, and guitar to the unit to be effected. In this case we would use the mixer's effects send (also called the auxiliary send) rather than an insert point.

There are many creative uses of insert points and effects sends, particularly when they have been extended to a patchbay. This creativity is gained by engineers who have experimented with different methods of connection and the different permutations of effects and processes. This creative outlook can be passed on in the teaching process and we hope to talk more about it in future in this column.

A QUESTION OF TIME


What is the difference between SMPTE and EBU timecode standards or are they just different words for the same thing?
Andrew Jobson
Southampton

Steve Parr of Wallen Parr Music & Production, who lectures at Gateway on MIDI and film music, replies:

When filming it is necessary to identify every single frame of film in order to avoid confusion when you subsequently edit the film together to assemble a final version for viewing. To this end the Society of Motion Picture and Television Engineers (SMPTE) devised a digital code to uniquely identify every frame of a piece of film - a timecode in other words. This code was designed to run from 0 hours, 0 minutes, 0 seconds, 0 frames and end at 24 hours, 59 minutes, 59 seconds, 23 frames - so that every frame of film over a 24 hour period could be identified.

Throughout the world, film is shot and projected at a rate of 24 frames per second (fps). However, due to differing television broadcast standards (PAL, SECAM, NTSC), video is recorded and played back at varying frame rates and so the timecodes have to be adjusted to reflect these different standards.

The European Broadcasting Union (EBU) has a rate of 25 frames per second, whereas the Society of Motion Picture and Television Engineers (SMPTE) in America has a rate of 30 frames per second. And, due to technical problems with harmonic distortion, a further version of SMPTE called 'Drop Frame' had to be devised which has a rate of 29.97 frames per second and is commonly in use in the USA.

Just as 'hoover' is used to refer to any vacuum cleaner, it is important to note that the term 'SMPTE' is often mistakenly used as a generic term to describe all timecodes. However, this is inaccurate and we should always differentiate between the four standards - SMPTE, EBU, SMPTE Drop Frame, and Film Rate.

MIDI PATCHBAY


My stockpile of MIDI equipment is beginning to grow - at what point should I consider buying a MIDI patchbay?
DS McCall
Strathclyde

Steve Parr replies:

The MIDI patchbay is a device that has a number of MIDI inputs and a number of MIDI outputs that can be routed to each other either by means of rotary knobs (like the Quark MIDILink) or by internal software programming (like the Akai ME30P).

The way it works is that you connect the MIDI outputs of your master synthesizer, sequencer and drum machines to the inputs of the patchbay, and the MIDI inputs of all your equipment, including aforesaid sequencer and drum machine, to the outputs of the patchbay. You can then assign different combinations of equipment to receive MIDI data from a selected source. This should be useful, for instance, if you wanted to record sequences from the keyboard using the internal tempo of the sequencer and then play them back according to the tempo of the drum machine.

Without a MIDI patchbay much plugging and unplugging of cables will be needed, and as one MIDI cable looks very much like another mistakes can and will be made. Also, much changing of connections can put strain on your connectors causing eventual failure of your leads.

One very useful benefit of a MIDI patchbay is that you can copy the output data from your master MIDI instrument into several MIDI inputs simultaneously, solving at a stroke any timing errors that you may have introduced when previously chaining instruments together via their MIDI Thru connections.

If you find that you are continually yanking cables about or have more than three instruments connected by their MIDI Thrus, then maybe it is time you bought a MIDI patchbay!

Further info about the full range of Gateway courses can be obtained by writing to: Gateway School of Recording & Music Technology, (Contact Details).



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Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - Apr 1987

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