Ashly DPX-100 Alternatives For Sound Installations, Recording, Broadcasting, Special Effects

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

if this type of transient doesn’t destroy a speaker outright, it may damage the speaker surround in such a way as to cause mechanical abrasion and future failure.

Alternatives For Sound Installations

To install a compressor/limiter in a sound sys- tem using a passive crossover, insert it between your mix- ing console output and the power amplifier input. For systems using electronic crossovers, there are two ways to use a compressor/limiter. It may be inserted between the mixer output and the crossover input, in which case it will act on the entire audio frequency spectrum. Alter- nately, if the limiter is inserted between an output of the electric crossover and the input of a power amp, it will only affect a specific band of frequencies.

Recording

The Ashly limiter can be used to prevent tape saturation in analog recording. Also, with modern trends toward inexpensive digital recording, it remains neces- sary to protect against input overload. With digital re- cording, the information stored on tape, hard disk, optical disk, etc., is either a 1 or 0, so actual signal level on the tape is not the concern it is with analog recordings, in fact it is not even a user controllable parameter. What is of concern however, is the signal level applied to the A-D (analog to digital) converters. If clipping occurs at the converter input stage, the resulting distortion is most un- pleasant, and will be recorded digitally as if they were part of the original audio signal, forever mixed with the audio. To prevent converter distortion while preserving the extended dynamic range of digital recording, look up the max input level of your recorder/converter and set up the limiter as follows:

1.Set Gain to 0.

2.Set Threshold to 2-3 dB below max converter input.

3.Set Ratio to 10.

4.Set Attack to 2 mS.

5.Set Release to .2 Sec.

6.Set Output level to 0.

If you are exceeding threshold frequently, your input signal is probably too high and should be turned down. Of course, every situation is different, so experi- mentation before final recording is always a good idea, but this is a good starting point.

To obtain a gentler limiting action at the expense of some dynamic range, decrease the threshold to -15 and the ratio to 3-5. This is also a good starting point for analog recording.

Broadcasting

Compression has long been used as a tool to make an audio signal appear louder. A good example is in broadcasting, where com-

peting stations with identical transmitters and power at- tempt to sound louder than each other. Since they are all restricted with respect to maximum audio level (modula- tion), their best tactic is to squeeze the dynamic range of their programs to just a few dB. The audio output level of the station virtually never changes, and the listener perceives this continuous high-level sound as being louder than the same material in an uncompressed form. Although both compressed and uncompressed programs reach the same peak levels, the compressed signal stays near peak level more of the time, and thus sounds louder. This tech- nique makes the broadcast more intelligible over ambi- ent noise, and increases the geographical area over which the broadcast is audible to the listener. Additionally, this compression technique is extremely useful for FM and infrared transmission systems for the hearing impaired.

8.3 Special Effects

Compression For Feedback Control

Acommon ritual in sound system set-up is equal- izing the room to remove feedback. This is generally accomplished by turning up system gain to purposely in- duce feedback, searching for the center frequency of the feedback, and then equalizing at that frequency to remove the feedback. Once this frequency has been cut, system gain is again increased to induce another feedback point, and the whole procedure is repeated until the engineer is satisfied that the significant problem frequencies have been corrected. The major problem with this approach is that the feedback can easily get out control, and the engi- neer ends up dashing back and forth between the mixer volume controls and the equalizer controls, while every- one in the room plugs their ears and prays it will end soon. The Ashly DPX-100 can turn this procedure into a fast, painless job, eliminating loud feedback levels and the possibility of speaker or ear damage.

Procedure:

1.Set up the DPX-100 limiter controls as follows:

a.Output level control to -20dB.

b.Input Gain control to 0dB.

c.Threshold control to -30dB.

d.Ratio control to infinity (∞ )

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