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BBE MaxCom [14/24] Operation
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10
bbE SECTION
In order to address problems inherent in basic loudspeaker design, BBE Sound, Inc. has developed a circuit that
has two primary functions. The rst adjusts the phase relationship of the low, mid and high frequencies. Since a
loudspeaker¹s natural tendency is to add progressively longer delay times to higher frequencies, the BBE circuit
adds progressively longer delay times to lower frequencies. This creates a kind of “mirror” curve to the time delay
curve in the speaker and neutralizes its distorting effect.
The second major element in the BBE system is the augmentation of the higher and lower frequencies. Loud-
speakers tend to be less efcient in their extreme treble and bass ranges. Most sound-reproducing systems
include a circuit for boosting high and low frequencies, showing an accepted awareness of the loudspeaker¹s ef-
ciency problem. The BBE system, however, provides a dynamic, program-driven augmentation which combines
with the phase compensation feature to restore the brilliance and clarity of the original live sound. The result is, as
one professional journal phrased it, “The most hearable advance in audio technology since high delity itself!”.
COMPRESSION EFFECT
At the beginning of this chapter, we dealt briey with the basic functions of a compressor/limiter. Now we will
discuss this point in more detail, with reference to the threshold setting, input level and compression: consider
an input signal which is applied to the inputs of two compressors. The threshold of the second compressor is
set 10 dB higher than the threshold of the rst compressor. Since a compressor only affects signals that exceed
the threshold level, it is fairly obvious that the signal of the rst unit, will be compressed more because as the
threshold is lower, it is exceeded to a greater exceeded before.
Furthermore, it is interesting to note that by comparing the input and output waveforms for the compressed
mode, the quietest sections of the input signal have been effectively raised in level, whereas the loudest sec-
tions have been effectively decreased in level. The overall effect is that both ends of the dynamics range have
been pushed towards the middle. The squashing effect of compression is important to remember and highlights
the major difference between compressing and limiting.
Compressing and limiting differ in one more aspect: the dynamic setting for attack and release times. For com-
pression purposes, a preferably longer attack and release time is generally the best in order to keep the overall
output signal within a specied dynamic range.
For limiting applications, considerably shorter times are necessary to control transient signals or to increase
headroom. To achieve inaudible compression, it is imperative to work with program dependent attack and re-
lease times and a Soft Knee response. The advantage of program dependent compression is most apparent
when processing musical material that is varied. The MAXCOM is suitable for all applications because of its
various time settings and the AUTO processor. With the AUTO switch engaged, the unit uses program depen-
dent attack and release times. When not engaged, the control times can be set manually. Please note, while the
AUTO switch is depressed the MAXCOM does not provide a limiter function even if the RATIO control is turned
fully clockwise because signal peaks are NOT radically cut off above the threshold point.
If you want to use the MAXCOM as an ultimate means of protection against overload, it is recommended to
study the following chapter.
THE LIMITING EFFECT
The attack time is dened as the time taken for a compressor to respond to program levels which have exceed
the threshold point. Because of the physical relationship between frequency and slew rate, the resulting factor is
that for relatively low frequencies a longer attack time was required than for higher frequencies: any unpleasant
dynamic distortion would be avoided. When compressing a program mix that includes a wide range of frequen-
cies, a compromise must be made when setting the attack time. This setting would generally suit the lowest
frequency components present. For general dynamic-range control using the compressor mode, this is of no
serious consequence. However, in a limiting mode, we are restricting the peaks of our signals to a maximum
operating level to avoid distortion in any subsequent devices. If we are using a conventional compressor in a
limiter mode, the result will be in very fast high frequency signal transients passing through unaffected by gain
reduction. It is therefore necessary to choose the limiter control times precisely in order to govern any kind of
transients. In order to use the MAXCOM as a peak limiter, it is necessary to operate the unit in limiter mode
(RATIO control turned fully clockwise) and to switch out the AUTO function. This enables the limiter function to
exclusively and instantaneously respond to signals which exceed the threshold level.
It is important that the AUTO switch is switched off and that the attack time is as short as possible to avoid any
audible distortion. The RELEASE control should be set to a value whereby side effects such as “utter” and
“pumping” etc. do not occur.
OPERATION
Содержание
- Safety related symbols 2
- Applications 11 3
- Audio input iii 3
- Contents 3
- Controls 5 3
- Installation 3 3
- Introduction 1 3
- Maxcom specifications iii 3
- Operation 8 3
- Rear panel 7 3
- Special applications 15 3
- The design concept 2 3
- Specifications 4
- Introduction 5
- Design concept 6
- The design concept 6
- Installation 7
- Installation 8
- 0 bbe process control 9
- Attack control 9
- Auto switch 9
- Bbe lo contour control 9
- Bbe on off switch 9
- By activating the auto switch the attack and release controls are disabled and the attack and release rates are automatically derived from the program material this function allows for unobtrusive musical com pression of signals or mixes with widely varying dynamics 9
- Chan on switch 9
- Controls 9
- Front panel controls 9
- Front panel layout of the maxcom 9
- Gate threshold 9
- Input level meter 9
- Output control 9
- Ratio control 9
- Release control 9
- Shows level of incoming signal in a range from 20db to 6db 9
- The attack control determines the rate by which the compressor responds to the signal which exceeds the threshold this control can be adjusted from 0 ms to 200ms 9
- The output control allows for the increase or decrease of the output signal by a maximum of 20 db thus a level loss due to the compression or limiting process can be compensated for 9
- The ratio control determines the ratio between the input and output level for all signals exceeding the thresh old point the ratio range can be adjusted from 1 1 to 11 1 limiter 9
- The release control determines the rate that the compressor returns to unity gain after falling below the threshold level this control can be adjusted from 0 5s to 4s 9
- This control adjusts the threshold level for the expander gate section in the range of off to 10dbu signals below the set level are attenuated 9
- This control is a low frequency adjustment for the bbe process it provides a boost of 10dbu when turned to its maximum position clockwise at 50hz when turned to its minimum position counter clockwise no adjjustment is taking place 9
- This control sets the threshold point for the compressor section it has a range of 40dbu to 20dbu 9
- This switch activates the corresponding channel the switch is used to make direct a b comparisons between original material and processed signal 9
- This switch engages the bbe process as indicated by the green led when in the out position the green led will not illuminate indicating that the bbe process has been disengaged 9
- Threshold control 9
- Front panel controls 10
- Rear panel 11
- A downward expander automatically reduces the overall level for all signals below the threshold the expander therefore operates in the opposite way to that of a compressor limiter expanders generally function with a flat ratio curve in that the signal continually fades noise gates however can be seen as high ratio expanders if the signal falls below he threshold it is radically attenuated 12
- Compressor section 12
- Expander gate section 12
- If the threshold control is set fully clockwise this corresponds to a threshold level of 20dbu in practice this threshold level cannot be reached as the unit would overdrive this control setting allows the compressor sec tion to be put out of action if for example the expander gate is to be used independently 12
- In the maxcom control of the dynamics process is achieved by means of a high quality vca with an operating range of more than 60db i e the input signal level can be reduced or increased within a range of 60db input signal levels below the adjusted threshold are not reduced however as soon as the input signal exceeds the threshold level dynamic control is activated the amount of compression gain reduction is proportional to the amount by which the input signal exceeds the threshold 12
- Operation 12
- Ratio control 12
- The adaptive expander is therefore equipped with a soft interactive nonlinear ratio curve which is best suited to human hearing critical signals in the vicinity of the threshold level are processed with a minute expansion ratio whereas signals that reduce in level will be subjected to an increasingly higher ratio which will result in greater attenuation 12
- The degree and type of compression is determined not only by the threshold control but also by the sub sequent ratio attack and release controls and by the auto switch 12
- The maxcom is equipped with a newly developed adaptive expander the ratio of which is automatically ad justed dependent on the program material the response characteristics of conventional expanders tend to cut into the signal abruptly and the result of this is unacceptable most of the time gain changes become audible 12
- The ratio control determines the ratio of change in output level compared to input level for all signals exceed ing the threshold the scale of the ratio is calibrated in db on the front panel it indicates the increase in input level required to produce a 1 db increase in output level in the introduction chapter we described the function of a compressor by comparing it to a volume fader where signal peaks are controlled manually in order to avoid distortions due to signals exceeding the threshold 12
- The threshold control determines the point at which a certain input level causes the level reduction to com mence the threshold control has an operating range of 40 to 20dbu 12
- The threshold control of the expander gate stretches across a very wide range and therefore applies to all working levels if the threshold control is turned fully counterclockwise the expander gate section is inoperative 12
- There are two ways to utilize this level control either the output level is limited in such a way that no signal can exceed a predefined maximum or the output level is reduced above the threshold so that signal peaks may well exceed the threshold but are reduced proportionally the extent of this change in dynamics is determined by the ratio control 12
- Threshold adjustment 12
- Threshold control 12
- Operation 13
- Operation 14
- Applications 15
- Applications 16
- Applications 17
- Auto switch in 17
- Control settings 17
- Final adjustments of the controls can then be made to suit your particular requirements including the ratio attack and release controls the auto function provides program dependent dynamic processing which suits most standard uses if a condensed or wider sound processing technique is required the attack and release times can also be manually adjusted 17
- For example a low ratio and very low threshold setting can be used to achieve soft and musical processing of the general dynamics of the program material higher ratios together with low threshold settings create rela tively constant volume levelling for instruments and vocals high threshold levels generally limit the overall level of a program 17
- In out switch in 17
- In the early 1960 s musicians began looking at the recording process as a way to create new sounds the pumping effect which had been avoided by earlier engineers suddenly became fashionable and was utilized 17
- Initial settings for the compressor section 17
- Noise reduction on effects paths 17
- Output control 0db 17
- Pleasant feedback problems if the maxcom is inserted into the mic channel it will shut off the channel when it is not being used reducing the possibility of feedback 17
- Ratio control 2 1 17
- Ratios greater than 6 1 effectively prevent the output level from signals significantly exceeding the threshold point provided that the output control is in the 0 db position 17
- Rotate the threshold control counterclockwise until an appropriate amount of gain reduction is indicated on the gain reduction meter this operation will be accompanied by an audible drop in output level the output control should now be turned clockwise to reinstate the output level the level of the unprocessed and the processed signal can be compared by pressing the in out switch 17
- The auto function prevents aggressive compression created by high ratios from sounding too unnatural 17
- The compressor function 17
- The effects rack is one of the most overlooked sources of noise in a pa system or recording facility the price of reverb and delay units and harmonizers has fallen drastically over the last number of years which have made these units a common feature in small studios and home recording installations however multiple effects units considerably increase the overall noise level so that the pleasure in acquiring a new sound effect is short lived it will prove useful to use the maxcom as the last component in the chain of effects units and use the noise reduction function of the expander gate section 17
- The experienced user will be in a position to specify parameters while in bypass mode and thus realize the effect before the unit is actually switched into operation this is important in live situations where a signal needs to be managed efficiently by the engineer without the convenience of continual a b comparison 17
- The maxcom as a sound effects unit 17
- The task of a compressor is to reduce the dynamic range of program material and to control the overall level the extensive controls of the compressor section provide a great range of dynamic effects from musical and soft compression to limiting signal peaks right up to extreme and effective compression of the overall dynamics 17
- Threshold control 20 db 17
- Applications 18
- Special applications 19
- Special applications 20
- Special applications 21
- You can use the maxcom to bring out an instrument solo or a lead vocal in a cluttered mix match the fre quencies of the equalizer to the frequencies of the instruments to be emphasized and for this it is best to use a notch filter with a high slope please make sure that in this application you only reduce the amplitude of the selected frequencies 21
- Special applications 22
- Service warranty maintenance 23
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