Dual/Stereo Broadcast Compressor/Limiter Operation Manual August 2004
CONTENTS 1. Introduction Page 2 2. Installation Page 3 3. Warranty Page 5 4. Description of controls Page 6 5. Applications Page 8 6. Specifications Page 14 7.
1.0 INTRODUCTION The BCL20 is a stereo compressor-limiter with a de-essing capability which allows the end user to process two different signals or one stereo program. Applications include : FM transmitter protection, disc mastering, SPL limiting in PA and discotheque applications, tightening of drums and sustain control on guitars and bass. Main parameters, parameters including threshold, gain, attack and release times and compression ratio are user controllable.
2.0 INSTALLATION IMPORTANT: PLEASE READ THIS SECTION BEFORE USING THE BCL20 2.1 INSPECTION AND UNPACKING The BCL20 has been carefully packed at our factory in a carton designed to withstand handling in transit. Should the unit appear to have been damaged in transit notify your dealer immediately and do not discard any of the packing. The carton should contain • The BCL20 unit • Power cord • Operator Manual (this book) 2.
faults and as such will not normally need replacing. If you think you have a power related problem please refer to your dealer. The voltage and fuse rating have been factory set for 230V 220V 115V 100mAUK 100mARepublic of Korea 200mANorth America • The correct voltage and fuse rating is indicated on the rear panel. • Please check that your unit is correctly rated for the voltage of the country of operation. If the fuse requires changing at any time please ensure the correct fuse is fitted.
BCL20 rear view showing Channel 2 and Mains connections The input and outputs of the BCL20 are on XLR connectors. For balanced input and outputs, connections to the unit should be wired as follows: XLR +4dBu Pin 1 Pin 2 Pin 3 Screen (Signal ground) Hot (+ve) Cold (-ve) For unbalanced operation join pins 1 and 3 on either input or output.
4 DESCRIPTION OF CONTROLS GAIN REDUCTION DISPLAY This 12 Led bargraph indicates the amount of compression (in dB). The law is expanded at low values. LEVEL DISPLAY This 12 Led bargraph indicates either the input level or the output level as selected by the input/output toggle switch. The bargraph can also be switched between peak and VU BYPASS This switches the compressor in and out of circuit, so that comparisons may be made between the compressed and uncompressed signal.
THRESHOLD This adjust the signal level above which compression occurs. The lower it is set, the greater is the compression. The threshold range is from -40 dBu to +20 dBu. ATTACK This determines how fast the compressor will act upon the incoming signal. This time may be varied from between 0.1 milliseconds and 70 milliseconds. (Caution : Very fast attack times introduce distortion at low frequencies with ANY form of compressor. This is caused by a low frequency signal being longer than the attack time.
POWER (On rear panel) This switches the unit ON or OFF and the adjacent led lights when the unit is ON 5 APPLICATIONS DEFINITIONS OF TERMS USED Compressor : A variable gain amplifier whose gain decreases as the input increases beyond a threshold point. A compressor uses ratios of up to 8:1 Limiter : A limiter is a compressor with very high compression ratios, usually above 10:1. A high ratio maintains an almost constant output level despite large changes in the input level above the threshold point.
compressor ONLY acts upon those frequencies and passes all other ones. GENERAL The usual purpose of Limiting and Compression is to increase loudness and to provide overload protection and generally to control level. Limiting Limiting is used mainly to provide overload protection ; i.e. to limit the output to some desired output level. The protection required is usually against transients which exceed the peak input level required for a tape recorder or a transmitter.
be necessary to either reduce the times used or reduce the ratio depending upon the effect required. Modulation If more than about 6db of compression is used, it is desirable to treat individual sound sources or groups of similar sound sources separately in order to avoid modulation effects, when a dominant sound modulates the rest of the signal. It is particularly difficult to limit low frequency sounds in a final balance, because the effect on the remaining signal and ambience will be most noticeable.
As an alternative, one can emulate such a filter, using a stereo one-octave equalizer set in such a way that the frequency response approximates that of figure 2. Fig. 2 THE BCL20 AS AN ACOUSTIC NUISANCE LIMITER : This is a complementary aspect of loudness limiting, but in this instance, the sound pressure level which must be limited is one that remains after attenuation and conduction outside the room or building where the sound is produced.
When this is done, one has to copy the frquency response to a graphic equaliser which is inserted in the side-chain. THE BCL20 AS AN AUTOMATIC VOICE-OVER (DUCKER) : This application is useful in discotheques and radio where it provides an "automatic fader" which reacts to the voice of the disc-jokeys, reducing the background music accordingly. To do this, the music channels must be routed to separate groups which will be processed through the BCL20 and then reinjected to the Mix busses (sub-group).
The following two applications show the BCL20 inserted into an individual channel. After processing, the signal is mixed with the other channels. This is done because the BCL20 is used to modify a sound, not to control its amplitude. Bass Drum Vocal The next two applications show the BCL20 connected at the output of the mixer. This is because if the BCL20 was inserted in the Mix inserts the level would vary with the setting Of the Master fader.
6 SPECIFICATIONS Frequency Response 20 Hz to 20 kHz +/- 0.5dB Signal to Noise Ratio + 4 dBu Input, + 4 dBu Output -94 dB Input Impedance 20k Ohms balanced Output Source Impedance 20 Ohms Output Load Impedance 600 Ohms to infinity Maximum Input Level + 20 dBu Maximum output Level 600 Ohms Load, 1 kHz + 20 dBu Total Harmonic Distortion (THD) + 4 dBu Output, 1 kHz, 10 dB compression 1 kHz, by-pass 0.07 % 0.01 % Intermodulation Distortion 0.
DS Action 12 dB at 8 kHz Input Connector Output Connector XLR 3 pin balanced XLR 3 Pin balanced Dimensions 483mm W x 190mm D x 44.5mm H 19"W x 7.5"D x 1.75"H Weight 3.9kg, 8.6lbs Shipping Weight 4.8kg, 10.6lbs Temperature Range Operating 0C to +50C Storage -30C to +75198>C Note: In these specifications, 0 dBu is referenced to 0.775 V RMS LA Audio reserves the right to alter any feature or specification without prior notice.
