DaviSound TB-2
"DaviSmart" Two Channel Line Level
Optical Compressor
Copyrights 1998-2006 © by DaviSound


2006 TB-2 Revised Layout

The TB-2 is a line level compressor amplifier using an optoisolator as the gain control (attenuation) device.
Our current "DaviSmart" design was inspired, initially in the early days, by the infamous "LA-2A" of the "old days". But, we took the concept so much further and, then, married it to state-of-the-art technology with opto-isolator componentry. The result is, we think, the best multi-purpose audio compressor ever designed with "speed of light" attack time and moderate, signal dependent, variable decay time.

What you see is what you get ...

The front panel "COMPRESS LED" shows the amount of compression being employed beginning with just a slight flicker and increasing to brighter, more sustained, display as the COMPRESS CONTROL is advanced.

Unlike comparator driven displays which are, in effect, simple A/D converters, this display is a TRUE ANALOG of the compress drive signal thus giving a better "feel" for the intensity of the amount of compression being employed. However, that being the case, it will not be highly visible from a far vantage point. It is advisable to adjust the control with an eye directly on the LED during preliminary adjustment. You will then be able to see peak gain reduction early on (a slight flicker on signal peaks), long before any compressor action is audible, while the COMPRESS CONTROL is being advanced.

TECHINCAL SPECIFICS of the MP-3 "MasterPiece" Compressor Module

  • Overall amplifier gain +20 dB
  • Available Gain Reduction - over 30 dB
  • Channel matching characteristics +/- 1 dB
  • THD at 1 KHz, recover control full CCW, 20dB of compression - under .08%
  • THD at 10 dB compression - under .01%

  • The compression control settings and resulting affects are input signal dependent so there are no hard,
    fixed position indicators.

    However, were the control turned fully clockwise, the chain would be operating with over 30 dB of gain reduction!

    Typical MAXIMUM settings of the "comp" control would be somewhere around 12 O'Clock (knob pointer straight up) which typically results in 10 to 20 dB of gain reduction depending upon the input signal peak/transient content. The extra reserve of the "comp" control is there if you need it as described further below.

    By nature, all compressors, or any processor that alters the incoming signal in some fashion, are inherent signal "colorers" of a sort. To fully assure yourself of the integrity of a TB-2/TB-3, carefully examine a quality sine wave through-signal at various levels and settings on an oscilloscope. YOU WILL NOTE EXCELLENT SINE WAVE SHAPE AT ANY SIGNAL LEVEL, FREQUENCY SETTING, OR COMPRESSION LEVEL. THERE IS VERY LITTLE DISTORTION EVEN AT DELIBERATELY EXTREME LEVEL SETTINGS!

    While the on-board LED "comp indicator" is quite sufficient to provide an exact visual analog of the compressor chain in action, detailed results can be measured on any down chain VU meter in your system (recorder input meters for example). With a 1 KHz sine wave input to the TB-2 and the "recover control" set for approximately 10 dB of gain at about 12 O'Clock, as the comp control is advanced, you can observe the logarithmic gain reduction "action" characteristics, for a steady sine wave, displayed on the VU meter.

    If using models with the specially, custom ordered "gain reduction" VU meter display, the inherent decay characteristics (release) of the particular setting respective to signal input may be observed when the signal is abrubtly removed.

    Since early compressor designs reflected the applications and required use of their day, they often included "stereo cross linking". This was considered especially useful for one of their main purposes, disc mastering, in preventing cutter groove "worble".

    The "DaviSmart" principle does not subscribe to "side chain" or "stereo linking" application! We maintain that both channels of our dual unit can be better, properly, manually adjusted for optimum stereo application, when required, accurately processing stereo program material far better and more faithfully than if cross-linked in older, traditional "stereo" compressor application.

    Nowadays, when most "bottom end" and heavier bass transients are "centered" and common to both channels, "stereo" linking, where one channel's transients and signal weighting affects the other channel, is considered far too un-natural and undesirable to be of any merit when accurate tracking can be better performed, and matched, invididually and manually with the "DaviSmart" comp control and recover settings.


    About COMPRESSION in general ...

    The more one understands one's tools, the better to use them for the job that is required. It is toward that end, of better understanding, and, thus, better application, that we offer an extensive general discussion of compression, along with specific information regarding our methods for acheiving it.

    Compression is just what the word itself implies. The dictionary defines COMPRESS as: "condense, constrict, densify, squeeze" ... to decrease, shorten, thicken. Well, in relation to audio dynamic range, ALL of these adjectives apply when audio compression is added in varying degrees!

    Most all audio compressors do, essentially, the same thing. The thing that varies is the specific way in which the various designers go about acheiving similar results.

    Compressors work on a GAIN REDUCTION principle. They usually employ a rather low-gain amplifier front-end with some form of automatic, variable gain control. This control is VOLTAGE VARIABLE. The more voltage this stage receives at it's control point, the LESS GAIN the amplifier produces. This voltage controlled amplifier, or voltage controlled attenuator, as the case may be, enables a compressor to be designed by sampling the signal passing through this stage, amplifiying and processing the sample, and sending it back to the control element to reduce the amplifier's gain.

    Now, the more this process is applied, and the greater the amount of compression drive that is utilized, then, the higher the RATIO of input signal to output signal becomes. In terms of decibels, a 10:1 ratio would imply that an input change of up to 10 db would result in an output change of only 1db.

    If enough gain reduction drive is employed, the compression ratio approaches infinity. This means that we have, at that point, amplified our sampled signal as far as we can and driven it back into our gain-reduced amp as much as we can, to the point where there is very little dynamic range left in our "squashed" signal to make any difference!

    All audio signals have a noise floor and a maximum peak ceiling. If we operate too close to the noise floor, our signal to noise suffers. If we operate too close to the peak ceiling, we're in danger of "bumping the ceiling" and CLIPPING our signal. "Clipping" is the point where an amplifier, or system, simply "runs out" of gain and headroom and the signal peaks begin to flatten causing very harsh distortion. The whole idea behind compressors, and peak limiters, is to reduce the dynamic range. This may be done either very slightly for practical reasons (as in peak limiting) or in very large degrees for a desired special effect.


    It's all relative ...

    No matter how one might TRY and isolate them, ALL of the parameters of audio compression are, actually, inherently very inter-related and inter-dependent. These parameters, such as RATIO, THRESHOLD, ATTACK AND RELEASE, are not only inter-dependent within themselves but, also, with the many,varied characteristics of the input signals as well!

    Our designs were among the first to take advantage of these inherent properties of signal dynamics. Our tests and developments in these areas allowed us to ultimately create a circuit design that would AUTOMATICALLY self-scale ALL of these parameters in the best relation to each other, based on the constantly changing qualities of the input signal itself, in a musical, sonically pleasing manner, as compression is applied with one, single control! Thus, the "smart" compressor was born!

    Our COMPRESS control, used in conjunction with the RECOVER control, essentially handles ALL of the parameters required based on the input signal sample. As the COMPRESS control is advanced from "full-off" to further on, in clockwise fashion, it causes both a lower THRESHOLD of signal action and a higher RATIO of dynamic range compression, simultaneously. As the OPTICAL ATTENUATOR reduces the gain of our signal as a result of this action, it becomes necessary to raise the overall "squashed" signal elsewhere in the chain to a higher AVERAGE level. This is accomplished with the RECOVER control which is actually a variable gain control to our final buffer amplifier stage.

    It is important to note EXACTLY what we are doing when we advance both these controls into action. We are, actually, reducing our PEAK level well below our CEILING level and, thereby at the same time, raising our system FLOOR where noise, distortions and signal "nasties" reside!

    To any audio purist, the question naturally arises, "Why would anyone want to deliberately LOWER dynamic range, the very thing that gives amplified audio it's approach to natural sound?"

    That's a VERY good question!

    In the early days of recording, it was desirable to employ limiters to avoid saturating tape, and amplifiers elsewhere in the chain, with limited headroom. Some people actually started to like the "sound" of this process even to the point of over-using it when it was not required for practical purposes.

    It would give an "up-front" presence to vocals and certain instruments in a busy mix causing them to sound "louder". Vocals and electric bass were, particularly, much easier to capture and record with fairly high compression ratios. Many artists began depending on the action of a certain type compressor/limiter for their mic technique and resulting "sound signature"! This became so "faddish" that it got to the point where a studio had to have a certain type compressor in the chain in order to record certain artists or the artists would go elsewhere!

    Processing of this type was carried to even greater extremes in broadcasting (and still is today!). AM broadcasters, in particular, almost always over compressed their signals for a variety of reasons. First, it gave them the maximum peak output power allowed by law since they could modulate their carrier signals right up to the very limit without overmodulating or "splattering".

    Next, since over-compressed signals sounded louder (actually harsh and fatiguing to many listeners!), they seemed to "jump out at you" in car radios which many program directors thought/think was/is desirable. In early Top-40 radio, it became "in-vogue" to see whose station could be the loudest on the dial!

    In the serious recording studio, compressors can be most useful tools since they allow, to some extent, a "set and forget" approach to recording certain tracks. Thus, they can become a second pair of hands with a lightning speed brain/reflex control system! On some instruments, such as electric lead guitar, they can be "overused" at times for good purpose by adding sustain and "bite". io.

    Rules of thumb (and fingers) ...

    In general, when adding compression to an OVERALL MIX, or to an AUDIO PROGRAM, considering what we've covered so far, the LESS compression added, the MORE NATURAL things sound!

    Our compressors start out so audibly subtle in their initial action, that you need a peak indicator, or subsequent chain stage VU meter, in order to SEE what they are doing before you can actually hear any effect at all.

    If OVERALL compression is desired for a general program mix, it is usually best to use a small amount so that signal peaks are limited but the more subtle sounds are unaffected. This can easily be accomplished with the TB-2 by advancing the COMPRESS control to the point where the compress indicator LED just begins to flicker on signal peaks. If more compression is desired, the control might be advanced to the point where compression just begins to become audible and, then, backed off slightly.

    On the other hand, for isolated instruments and voices when laying tracks in the studio, higher compression settings may be desired. Electric bass is almost always "tightened up" with a fairly high compression setting. Vocals usually require moderate compression settings varying, of course, from one performer and performance to the next.

    Action ...

    Remember the little old lady who always drove thirty miles an hour no matter where she went but insisted that she have the horsepower under the hood just in case she needed to get from thirty to sixty in just a couple of seconds?

    Our COMPRESS control is designed much the same way.

    It begins at a very high signal "threshold" with the incoming signal and initiates about a 2:1 compress action. ATTACK and RELEASE are always automatically self-scaled according to the previous parameter settings AND the required handling of the musical dynamics present in the signal itself.

    The COMPRESS control reacts VERY QUICKLY as it is slightly advanced. At about 8 or 9 O'Clock, things begin changing rapidly. The ratio quickly increases to about 5:1 and this, in turn, lowers the threshold of operation. At around 10 to 11 O'Clock the action of the control begins to become more "hair trigger" (to provide all the built-in user leeway described earlier). By the time we get around to 3 O'Clock with a typical incoming signal, we are approaching infinity as our signal has become so "squeezed" that there is very little difference in the sound as the control is advanced to the extreme setting.

    So, like the car that goes from zero to ninety in one swift press of the accelerator, our single control takes you from zero to infinity in compression in less than one full rotation. This can sometimes make fine adjustment a bit tricky but, with a little practice, and with the help of the LED compress indicator, operation of a"DaviSmart" Optical Compressor quickly becomes second nature!

    You'll find most of the applications require compress settings well below 12 O'Clock. Actually most of the required settings will range between 8 O'Clock and 11 O'Clock but, like the extra, reserve automobile horsepower, the extra compression action is available from this one control for those occasions when you might want to apply it.

    So, you can see, there is enough leeway designed in to allow you to OVER -use the compressor easily. The design is, intentionally, NOT FOOLproof! It has to be applied discriminately, and wisely, but such should be the case with any professional tool. The point of all this precaution is simply this: NO other product that you may be used to offers you as much "action" from it's controls as the TB-2/TB-3 COMPRESS control places at your disposal. So, get used to a lot more "action" from within one rotation and learn to use it judiciously!

    "Garbage IN... Garbage OUT" ...

    That old tech saying takes on a veryemphatic meaning in regard to audio compression. Actually, it becomes, "Garbage in, ever INCREASING garbage out!". This is because, if there are is "dirt" lurking anywhere within the signal, compression will certainly bring it up to where it can be heard or "felt".

    The TB-2 / TB-3 design can also be used to advantage in program processing application for live sound and for broadcasting. However, it is in these applications where the aforementioned extra compression action provided must be most carefully taken into consideration. For example, it would likely be disasterous for a program director, or station engineer, to put one of our compressors on-line and simply turn the controls "wide-open" as they sometimes do with other products! But, operating within the 8 O'Clock to 10 O'Clock setting range of the COMPRESS control will yield an excellent, high quality broadcast program "processor".

    Likewise, using a TB-2/TB-3 for live sound,ahead of the final amplifier stack, will allow driving the system at a much higher AVERAGE level without fear of peak clipping. This is easily set up by turning the compress control up to the point where the LED indicator is just flashing on peaks. This will normally be with the control just "cracked", somewhere between 8 O'Clock and 9 O'Clock.

    Once again, going too far beyond this setting on program material will result in increasingly un-natural sounds as the distortion floor of the overall program is raised to near peak level by over-compression. Of course, all competent professional sound engineers will be aware of this and would detect any audible artifacts of such a setting long before their audience.

    Integrity and Security ...

    We've gone to great lengths in this manual to emphasize the potential for MIS-use since no other compressor design, that we know of, has ever offered the user anywhere near as much processing from one single control as does the "DaviSmart" design. Perhaps, since we've considered so much "negative" with all the precautions, we should dwell, in closing, on some of the many, numerous POSITIVES you can expect from your unit!

    A lot of this "positive" will be apparent as soon as your ears respond to the signals passing through your unit! The silky, transparent compression action, when properly adjusted, will naturally speak for itself. You will hear no undesirable compression artifacts. One reason we spend so much time going over the powerful COMPRESS control action, is because the novice user will often "crank" the control until he/she hears some "hard compression". At this point, the TB-2 is probably OVER compressing, especially on mixed program material! This is because it does it's thing largely UNNOTICED in a very transparent fashion when properly adjusted and applied!

    Part of the FUN of trying out your new unit is to watch the gain reduction and compress action taking place on a downchain VU meter long BEFORE you can HEAR anything like traditional "compressor action"!

    As with all DaviSound products, you can be assured of the most knowledgable and careful circuit designs, component selection, application and circuit construction techniques to guarantee and assure signal integrity. You would expect no less when entrustuing your archive quality material to any processor and neither would we (please refer to our "Design Philosophy" page for more information in this regard).

    After you have lived with your compressor and truly come to know it's capabilities, you will never want to be without one, or several (some use them on every track of a mulit-track format!) during any recording session ever again!

    "Glowing "DaviSmart" USER Testimonials" ...

    Here are some comments from fellow users, excerpted from written statements in our files:

    "I'm now recording vocals in a way I've never been able to acheive before ... " - S., Madison, Wisconsin

    "I love my TB-2 on bass! I've found I can actually patch my Fender Jazz direct ... and get enough (signal) to use it ahead of the rest of my system ..." -D., Atlanta, Georgia

    "It took a little while to get used to all that response in the compress control, but now I love this box (TB-3) ..." - C., Fort Payne, Alabama

    "I like to detect the small changes from one slight position (Compress control setting) to the next. But, when I do bass, I just set it mid way and go ..." - K., Virginia Beach, Virginia

    "I keep mine (TB-2) in the line all the time. My board puts out -10 db but my two track needs +4 db in. I can do this easily with your recover control and still use a touch of compression when I want to ..."-G., Coos Bay, Oregon

    Additional written specifics about your unit are included inside the box at shipping.

    Thank you for owning a DaviSound TB-2!

    Please let us hear from you regarding your application of your unit!

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