E85.1810: MIDI for NON-MAJORS
Managing Sound: Studio Equipment

© Copyright 1997-98 John V. Gilbert All Rights Reserved

Although the focus of the course is on MIDI, we have to understand basic ideas of a studio set up in order to optimize the results of our MIDI work. After all, one of the prime objectives is to make music on the computer. The computer needs considerable help from the studio equipment. Minimally, we need amplifiers, speakers, and the various cables to connect the equipment. As a studio grows and adds additional sound models, effects processors, a mixer will be come an essential piece of equipment. As with the MIDI signal, where we are concerned with the MIDI IN aand MIDI OUT and the path of the MIDI signal, we also need to understand the signal flow of the audio path. In general, synthesizers must be connected to an amplifier connected to speakers.

Amplifiers

Some studios may use integrated amplifiersthat include "pre-amps" which enable the user to select different functions that accept different inputs from peripherals such as cassette players, CD players, etc. This is often true of a small studio, especially if there is no mixer. In general, such integrated amplifiers have inputs on the rear panel that accept RCA connectors from phonographs, CD players, cassette players, DAT players, video sources, etc. The front panel will have some means of selecting these various inputs at any one time. There is often a jack in the front for a microphone.

Power amplifiers may be found in larger studios, especially with a mixer. "Preamps" may also be used with a power amplifier to serve the function of selecting different peripheral devices which will be amplified. The rear paanel has inputs for a single source and the fron panel usually has only controls for the audio level of each stereo channel. Some power amplifiers will also have some sort of metering device to track with the sounds are too loud and will have a "clipping" mechanism to prevent damage to the speakers should the volume be too loud. Many studios will not use a preamp, but will utilize the mixer to select devices, since the mixer provides multi-device access to the power amplifier.

Speakers

There are many, many speakers available at every conceivable level and price. In general, studios use what are described as studio monitors which are a moderate size speaker with a flat (i.e. no boost to trouble or bass sounds) response. Selecting speakers are a matter of personal preference, and although it is generally true that more expensive speakers are of higher quality, there are many excellent sp[eakers at a moderate price range. Some studios like to mix on several different size monitors to hear what the music would sound like on a boom box or a car stereo.

Of course, speakers are at the end of the audio signal path connected to the amplifier by speaker cables. Location of speakers is important in hearing the sound, especially in achieving reasonable stereo separation. It is wise to keep the speakers suspended and away from the studio equipment and computers. There are speakers which have built-in amplifiers known as "powered speakers" which have been designed for multi-media use with computers. An attempt has been made to shield the magnets of the speakers so that they will not interfere with the computer.

Cables, Connectors, Adapters

Cables and connectors along with adapters are the essential links between the various audio devices. In addition, we have MIDI cables that will enable keyboards, synthesizers, and other audio devices to send and receive MIDI messages. It is important to understand that each of these connectors and jacks have two components:
(l) one part of the connector is to provide the signal,
(2)the other part is to provide the "ground."

The "ground" is an essential function in audio (an in electricity, electronics, etc.). If units are not properly grounded, one can hear a "hum" in the speaker. A lightning rod is a form of a "ground." Lightning rods divert an electrical charge harmlessly into the ground. All connectors and receptors have the signal and the ground built in so that signals eventially reach some part of the chain where the charge is released.

There are several types of connectors and you should familiarize yourself with the types of connectors and their receptors. The table below gives you the most common collection of connectors in use today.

Several Types of MIDI and Audio Connectors

MIDI Cable







MIDI Connector







MIDI Receptors



Phone Connector

RCA Connector





Mini Phone
Connector




These cables and connectors need to be matched. In general, phono jacks are used with mixers, and most amplifiers use RCA connectors. A great deal og home equipment, including personal cassette players, and mianturized equipment use the mini-phone connectors. The mini-phone connectors are also used with most computers and computer peripherals such as microphones and external computer speakers.

Because there are so many cables in a studio which inevitably become tangled, many studios use cable configurations which are color coded and are wrapped together. This bundling of different cables is called a "snake."

Mixers

Mixers become the heart of a sound studio, bringing together a number of audio devices in which the sound levels can be mixed, effects (such as reverb, digital delay, chorusing, etc." can be added, and sound "equalized" through boosting of specific frequency ranges. You can experiment with these effects to see how they affect sound through most digital audio recording programs on the computer such as SoundEdit16.

The mixer pictured here is a 16-track mixer which can mix down to 4 tracks or to stereo or even mono, if desired. Essentially, the slide switches on the left control levels for individual devices or stereo levels. One stereo audio device would use two slide switches, so this mixer could handle up to 8 stereo audio devices.

Many mixers are now capable of being controlled by MIDI messages. This allows the user to "program" the mixer for the conditions of a specific musical work and to raise and lower volume levels throughout the piece as needed. Many sequencers now build in mixers into the computer program which in effect provides the user with a virtual mixer that can be quite powerful.

Signal Path

In audio, the signal path is quite simple. Audio devices will have outputs that go into the matching inputs on an amplifier, or in designated slots on a mixer. In generalthe signal is traveling from a sound source, through devices such as mixers and effects, to the amplifier which is connected to the speaker.

Treatments (Aux)

The treatments on the mixer itself are usually limited to equalizing the sound and controlling the audio l;evels of each channel of each device. Other treatments are added to sound with the mixer by using the auxillary send and return connections on the mixer which allows you to add an effects processor in which the sounds are looped through the processor back to mixer.

There are several kinds of signals that are processed by mixers. The line inputs from most audio devices are low impedance, which from a practgical standpoint means that longer lines can be used to connect modules without causing difficulties. Some microphones are "high impedance" which means that there can be difficulties with longer cables. Mixers often include inpuits for low impedance and high impedance. In addition, some lines are balanmced and unbalanced, depending on a number of factors, including whether or not the microphones use transformers. Going into detaiul about these factors are well beyond the limits of the course. You should try to be aware of these differences when the doicuments accompanying peripherals specify impedance levels.

Ins and Outs of Connecting

The audio signal path is very simple. Essentially the output of the sources for sound are connected to the inputs of the mixer. The mixer outputs go the in put of the amplifier which distributes the signals to the stereo speakers. Just remember that outputs must go into inputs and vice versa and you will not have trouble connecting the various sound devices. The diagram below shows the various sound devices with their stereo connections to the mixer. The mixer is looping the sounds to an effects processor. The keyboard is serving as a synthesizer and as a controller of two sound modules. The mixer is connected to the amplifier.

Audio Signal Path

Copyright by Prof. John V. Gilbert

Send feedback or questions to gilbert@is2.nyu.edu