Xl-300 Compressor Oil Equivalent

[Samantha Figueredo]

TheNASH 2BE4 liquid ring vacuum pump and compressor series have been optimized to deliver a 6-8% efficiency improvement over previous 2BE models. Based on the proven reliable flat sided liquid ring vacuum pump design the 2BE4 has a polyisoprene lined body, flexible inlet and discharge connections, and a large inspection port for improved performance and reliability. With capacity ranging from 1,950 to 32,100 m/h (1,150 to 18,900 ACFM), the 2BE4 is well matched to demanding environments like the paper, power, mining, and chemical process industries.

The 2BE4 liquid ring vacuum pump and compressor series is an upgrade to the proven 2BE3 model and has been engineered to deliver improved performance, reliability, and efficiency over the previous models. Compared to previous models the 2BE4 offers efficiency improvements up to 8% and has reduced maintenance requirements.

Some applications require vacuum and compression in one process. Instead of handling the gas with two separate machines, our liquid ring vacuum pump and compressor models can do the job with only one pump - reducing cost and simplifying installation.

The unique inlet configuration allows for both top and side inlet arrangements to accommodate low headroom installations. In installations where space is limited, the top discharge capability of the NASH 2BE4 allows the use of a top mounted discharge separator that saves floor space and eliminates the need for a trench. 2BE4 pumps are amazingly quiet during operation. Sound levels of 72 to 85 dB(A) (measured at a distance of 3.3 ft (1 meter) from the source) have been recorded for even the largest of the pump models.

Designed to operate in demanding environments like the paper, power, mining, sugar, and chemical process industries, these pumps offer durability and reliability at a low cost of operation. The standard polyisoprene lining on the pump body resists aggressive process gases and liquids to provide exceptional corrosion resistance. The polyisoprene lining also consumes less energy than the equivalent unlined pump. For added corrosion resistance, stainless steel internal components are available in certain models.

[3]A Compander is a compressor followed by an expander. If the time constant of the compressor and expander are the same (and the "channel" is perfect, i.e. linear and lossless) then a Compander is transparent. If you change the time constant of one vs. the other the transients will become distorted. The "Transients" knob controls the time constant mismatch. Negative values smooth the transients, positive values enhance the transients. A Compander with transient enhancement can be used on kick drums, bass, etc. to add punch. Transient reduction can be used to reduce plosives. For guitar you can use the Compander to add or remove pick attack.

[4]The first step in adding compansion to the delay block was creating a compander algorithm. So I created a Compander type first in the Compressor block. Once that was working I used that algorithm in the Delay block. The Compander allows you to set the Ratio, Time, Transients and Level. Turn Transients down and the attack is reduced, turn it up and the attack is enhanced. You can use it with kick drum to enhance the punch, put it on vocals to reduce plosives, etc.

[6]The attack time is actually dynamic and a function of the input level. Our algorithm models this. The default value is 3.6ms and is the maximum attack time. The higher the input level, the lower the attack time.

[9]Optical 1 uses a full-wave rectifier as a detector (peak detector). Optical 2 uses a true RMS detector. The LA-2A and many other compressors use rectifiers as detectors because it's easy and simple. Technically true-RMS detectors are "better" but they are difficult to implement in analog hardware. Whether or not true-RMS is better in actual real-world applications is debatable. There are those that claim that true-RMS detectors more closely replicate the natural compression behavior of the human auditory system. Peak detectors respond more rapidly to transients while RMS detectors have a smoother behavior. The only way to know which you like better is to try them.

[13]The Studio Compressor is really nice now. I compared it to my favorite hardware unit (dbx 266XL) and the Studio Compressor sounds and measures better (less distortion at low attack/release times).

[14]The compressors are great. If you are typically using pedal compressors like the Keeley then you want to be using the "Dynamicomp" type. The other types are studio compressors and won't sound/feel like what you are used to.

[18]Compressors distort. The shorter the attack and release times the more distortion. This is because a compressor works by doing y = x * g where g is the gain. As the attack and release times approach zero g approaches k * x so you end up with y = x * k * x which is obviously very nonlinear.

Compression is, by definition, nonlinear because it is not time invariant. The audibility of the distortion is a function of human auditory perception and the attack and release parameters. The shorter the attack and release the more we perceive the distortion.

[19]You shouldn't use a combination of low Attack Time and low Release Time. If one is low the other should be high. Otherwise the detector will not filter enough. This is the nature of compressors. We allow you to use low times but you should be aware that it can cause distortion. Very low attack times will result in detector chatter. This is the nature of detector circuits.

[20]I recommend turning Auto Att/Rel on. The Attack and Release controls still work but it uses some fancy math to vary the attack and release times as a function of data statistics. The only downside is that it adds a little CPU hit.

[21]The types with no Auto Makeup switch have inherent makeup gain in the algorithm. It's not something you can turn off now. If you've ever used a Dynacomp you'll notice the volume does not decrease when you increase the compression.

[24]You can use the Compressor block as a "Clarity" control. Set the sidechain high-cut to around 200 Hz. Now low notes will get compressed more than high notes. This will make the lows clearer when digging in. This is like a variable high-pass filter that gets more intense the harder you play. When you play lightly the compressor will do nothing. As you play harder low frequencies will have less gain than high frequencies.

[25]There is pre/de-emphasis on the compressor. That will change the compression character of the attack a bit. To simulate this use the Emphasis control or the filter parameters in the Sidechain page.

[27]The only thing auto-gain does is attempt to keep the output level the same as the ratio and/or threshold is changed. It has to make assumptions about the incoming level which is just a guess since every guitar is different.

The idea is that once you set it you don't have to adjust it as much as you would if you didn't have it. For example, the makeup gain can run anywhere from 0 to 30 dB depending on the settings. With Auto Makeup on you typically don't need to adjust more than +/- a few dB.

[29]It can't be turned off because it's inherent in the algorithm. Think about the classic Dynacomp. It doesn't calculate the makeup gain, it happens automatically due to the nature of the circuit. The algorithms replicate the behavior of the circuits.

If you're using multiple audio routings and need to align them, preventing timing differences (latency), you can use the Compressor block. Use the Dynamics type, set to a low ratio, adjust the Lookahead parameter.

Pumping is an effect that occurs when a sudden strong peak causes a compressor to reduce levels such that the entire signal audibly dips and then returns. The event that triggers pumping might be brief, and can be in any part of the frequency spectrum. To reduce pumping caused by low or high end spikes, you can use sidechain filtering to make the compressor less sensitive to such peaks. Very fast and very slow release times tend to make a compressor seem more resistant to pumping, but can bring issues of their own. Another possibility is to switch to a multiband compressor, which handles lows, mids and highs individually. Now, it cannot go without saying that pumping can also be used as an effect in itself, as when a kick drum is set up as a sidechain source to give electric guitars a bouncing sound common in dance and industrial music.

[35]Cascading compressors has been used in studios for decades. An 1176 into an LA-2A is a popular combo. The FMR Audio put this into a single package with their RNC (Really Nice Compressor) compressor which has two compressors in series. The "SuperNice" switch engaged a third stage.

To try this, use two Studio FB 1 compressor block in series. Set each one of them to a 4:1 ratio, you can set the first one in series higher if you want. Then set the knee to high or medium high and make sure the threshold is set on the first one in the series to SQUASH the signal by at least 6db+ of compression, if not more. Raise the level a few db to hit the second one, then set the level out of that one to hit the amp.

Use a very fast attack, try 0.283 ms attack (actual 1176 attack) and 75 ms release on each. Play with it until you get the sound you like. Lowell used a Tele bridge pickup put into his Strat, but you can use the squawk position or middle pick up on Strat if you like.

[36]I use "Analog Compressor" for Keeley sounds. It works great! Because I play vintage output guitars, I like to boost the level going in by adjusting the output of the input block before it. You can try "Auto Att/Rel", or use the published "classic" Keeley recipes*. Personally, however, I prefer a faster release, in the neighborhood of 75ms or less.

[37]I don't hear anything the Dynamicomp model isn't capable of (except for the noise). Turn off Auto Att/Rel. Set the Attack to min, Release somewhat high, Compression as desired and Bob's your uncle.

[38]The key is to use a feedback compressor. So that would be any of the pedal compressors and the Dynamicomp or the Studio FB Compressors. Then either set the threshold all the way down or all the way up if it's an upward compressor (Studio FB Compressor 2 IIRC). Set Attack Time to min, Release Time fairly long. Make sure detector type is peak and Auto Att/Rel is off.

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