The default setting is all to the right. If this control is all to the left, the compressor appears to be defective, since only 3 dB regulation can take place!

1. Use the ON Switch (29) to insert the module.

Limiter:

2. Set the Limiter Threshold control (1) all to the right

3. Set the Limiter Release control (2) to 0.3 sec.

4. Set the Limiter Attack control (3) all to the left

5. Set the Limiter Ratio control (4) all to the right

6. Set the Output Gain control (5) to 0 dB, or use a setting, meeting your needs

7. Leave the LIM Switch (6) unpressed for the beginning

Compressor:

8. Set the Crest Switch (8) to position 3

9. Set the Compressor Threshold control (7) to - 18 dB

10. Set the Knee Control (9) all to the left

11. Set the Envelope Control (10) all to the left

12. Set the Fill Control (11) all to the left - IMPORTANT SETTING

13. Set the Release Control (12) to 0.3 sec

14. Set the Release Law Control (12a) to EXP

15. Set the Attack Control (13) to 8 msec

16. Set the Ratio Control (14) to 2

17. Set the Dyn Color Control (19) all to the left - IMPORTANT SETTING

18. Set the GR-Limit Control (20) all to the right - IMPORTANT SETTING

19. Set the Static Color Control (21) all to the left

20. Set the Int Control (22) all to the right - IMPORTANT SETTING

21. Set the Gain Control (18) to 0 dB (Center)

22. Leave the REG-REV switch (30) unpressed

23. Set the AUTOGAIN REF control (18a) to 0 dB (Center)

23. Leave the S-C INS switch (16) unpressed

24. Leave the Autogain Off switch (17) unpressed

25. Switch on the Compressor (15)

Expander/DeCompressor/Pump-Up Compressor:

25. Set the Threshold control (23) to - 15 dB

26. Set the Release control (24) to 0.3 sec

27. Set the Attack control (25) to 6 ms

28. Set the GR-Limit control (27) to 10 dB

29. Set the Ratio control (26) to 1.6 (to the right)

31. Leave the EXP switch unpressed for the beginning (28)

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Quickstart

The following settings are only one example for an endless number of different settings. We are leaving out commonly used settings, since we assume that you are familiar with standard settings in the principle use of compressors.

Before you start trying, please make sure that the controls marked as IMPORTANT SETTING are set to the recommend initial positions. These settings control uncommon functions that you won't find in other dynamics units. Activating these controls in the beginning can cause confusing behavior of common settings, blur the effects of common controls, or simply block particular functions.

The following setting results in a natural sounding compression, that causes high loudness gain, but maintains the transients. It is based on the initial settings listed above. The text leads you thru the process of adjustment and will make yourself familiar with the special functions. After going thru this process, you'll have many own ideas how to use the special features differently.

Compressor

a) With common input levels, the initial setting should result in approx. 10 dB of gain reduction. Check the display for the actual gain reduction and adjust the Threshold control (7) to achieve 10 dB if this not the case.

b) Set the Attack control (13) all to the right. Now the attack time is so long that all transients will pass thru without causing regulation. Turn the attack control in little steps to the left. Find the position that maintains the natural impression and the transients but causes regulation to avoid the 'breakdown' of the signal after the peaks. You will end in the range between 8 and 16 ms with most common signals.

c) Try different positions of the Crest switch (8) and find the best suited setting for the particular mix.

d) Optimize the Release time setting (12). The relase time should be short enough to avoid audible pump up, but as close as possible to the point where pumping becomes audible. If the acutal setting causes no pumping, increase the release time a little (to .6 or .8 sec). If there is still no pumping add gain reduction by turning the Threshold control (7) one or more clicks to the left. As soon as you hear pumping reduce the release time (12) and find the point when pumping dissappears.

e) It is most likely that you will have low frequency distortion after fine tuning the release control (12). If not, use the Treshold control (7) and increase the gain reduction until you can hear LF distortion coming up. If you had to change the Threshold setting (7), check again for pumping and readjust the release control (12) if pumping is audible. (Just repeat step d in this case)

f) Open the Envelope control (11) until the low frequency distortion disappers.

g) Check the setting and compare the achieved loudness gain by switching the compressor in and out (15). Make sure that the levels of the compressed and the uncompressed signal are identical. Most of the gain reduction will be compensated by the autogain circuitry. If there is still a difference, use the Gain control (18) to adjust matching levels.

h) Try to fine-tune the setting by repeating the steps above, if you are not satisfied with the result.

i) You can now try to achieve a higher gain reduction, either by setting the Threshold control (7) more to the left, or by setting the ratio control (14) more to the right. A higher gain reduction will always bring up some negative side effects. At this points the main problem will be the 'demolition' of the signal structure due to the high gain reduction. Use the Fill control (11) and add the uncompressed input signal to cover the demolition. Focus on the fine structures of the signal and find a setting that restores the original without affecting the compression too much. If the Fill control (11) is wide open, you will loose loudness gain. Fill is a powerfull tool to achieve higher gain reduction without typical compressed sound.

j) You will now have a strong, but still good sounding compression with high loudness gain. However, the short release time that is necessary to avoid pumping will also result in a behavior that is 'tight and close to the signal'. Its about time to put some 'air' into it. Open the Int control (22) carefully. Int adds a long time integration modulation to the regulation. An additional control circuit generates a control signal from the envelope of the input signal, using long attack and release times. The Int control (22) adds this signal to modulate the release time. The release time changes a little as soon as the average loudness of the input signal is different. This makes the compression less tight; the mix sounds more natural. If you add too much Int, you will loose loudness, since the total release time is too slow to drive up the gain after peaks. The goal of using Int is to maintain loudness, but get rid off the tightness. Try to find this compromise.

ATTENTION: Int is a long time integration; the reaction on the setting is very slow! Change the setting in little steps and wait several seconds for the result before you change again. If you need to turn the control to left, it is a lot faser to turn the pot all to left for a second and than go to the new setting. This causes a reset to the circuit.

Options:

At this point you can try some more functions that might improve the result:

k) Knee (9)
Open the knee control and try if a soft knee setting is of advantage. The effect of a soft knee setting is high with high ratio settings, but lower with lower ration values, so don't expect a miracle.

l) Static Color (21) and Dynamic Color (19)
These controls add 2nd harmonics distortion to the output signal. The static color control (21) adds a constant percentage of distortion, while the dynamic color control (19) adds distortion that is proportional to the gain reduction. Using this control you will get more distortion with peaks, which comes close to the behavior of many vintage compressors. With many mixes, adding distortion is not of advantage. However, depending on the program material adding a little harmonics can produce a nice and interesting color. (The U794 Harmonics Distortion Generator offers more possibilities for adding harmonics.)

m) GR-Limit (20)
The GR limit control allows controlling the maximum gain reduction. Setting this control to 5 dB, for instance, results in a compression that stops at higher levels. This features is of advantage if you use a multi-compression; for instance if you use the limiter section for compression of the high level range with an entirely different setting. Adding 'pressure' and 'density' by raising the average level below the peaks is also possible; however, the pump-up compressot (see Expander section), is better suited for this purpose.

n) Regulation Reverse (30)
The compressor section is feedforward controled. The Reverse switch (30) selects feedback control instead. The behavior of the compressor changes with this setting; however, Threshold and Ratio settings are affected and the Gain and Autogain will now also alter the Threshold. The compression is closer to commonly used vintage compressors. In total with a setting as described above, feedforward regulation is better suited. However, with more conventional settings, feedback regulation can be of advantage.

o) Release Law (12a)
The Release Law (12a) controls the characterics during the release phase. With a setting all to the left (EXP) the behavior is exponential, which means that the increase in level is controlled by the discharge curve of a capacitor. In the beginning the level raises fast and gets slower the closer the value gets to the steady value. The other setting (LIN) causes that the level increases with constant speed. This setting will result in the impression of a shorter release time without the the release control (12) is changed. Both settings can be controlled from EXP to LIN with the pot. Try out, if another setting results in an improvement.

Pump-Up Compressor

The pump up compressor is one of three possible modes of the expander section. We start with this mode, since it can improve the above compressor setting.

The pump up compressor works like an reversed expander. It adds gain when the level drops below threshold. The regulation takes place only below threshold. Actually there is no lower limit but a GR-Limit control (27) that avoids that the pump up compressor raises the noise level too much. We have already prepared the section with the initial setting.

o) Switch on the section with the EXP switch (28)

p) Check for the gain reduction and readjust the threshold control (23) to get 6 to 9 dB of gain change on the display. The optimum setting depend on the structure of the signal but lets start with this value.

q) The pump-up compressor adds density in the low level range. The 'breakdown' of the signal is compensated. The big advantage is that the time constants of the pump-up section can be a lot faster than the time constants of the compressor, since only the low levels that are not sensitive against distortion cause high gain reductions. Alter the Ratio setting (26) to the right and to the left to find the best possible position. Focus on the density; you should get a result that seems to move the entire mix to the front.

r) Now change the release time (24) and try to find the best possible setting. The release time with pump-up mode is the time the compressor drives up the gain when the level drops. This time should be as short as possible, but long enough to avoid distortion. If no distortion comes up, set the control all to the left. Otherwise, find the shortest possible setting, free from distortion.

s) The Attack control is of minor importance with this mode, since it determines the time constant of reducing the gain when the level increases. Check in both directions, if a different setting is of advantage.

Expander

For mastering, the expander is of minor importance. Meaningful use of the expander is only possible if there is a high noise floor in the beginning, below breaks or at the end of the mix. The differences to the use as pump up compressor are:

t) the Ratio Control (26) has to be on the left side to operate as expander.

u) the Attack control (25) now determines the fade in time. It should be as fast as possible to avoid audible fade in

v) the Release control (24) determines the fade out speed. If should be set to 0.3 or longer times, if nessary. The noise should dissapear fast but not switched off.

DeCompressor

The DeCompressor can be used to repair over compressed mixes. The operation is similar to an expander; however, the threshold level has to be a lot higher. Usually the original parameters of the compression are not known; a try and error setting is necessary to figure out an appropriate setting for the particular mix.

w) set the Ratio control (26) to -1.6 (on the left side)

x) set the Threshold control (23) all to the right

y) set the GR-Limit control (28) to 10 dB for the beginning

z) reduce the Threshold level (23) until you get the impression that you've found the upper point of the over-compressed signal.

I) readjust the GR-Limit control (28) to determine original threshold level of the comrpession.

II) Alter the ratio setting (26) and try if another setting offers any advantage

III) Alter the Release (24) and Attack (25) controls to improve the result

IV) Repeat the entire process and try to optimize

Limiter
V) Wait with the Limiter Setting until all other settings are completed.

VI) Switch on the Limiter (6) and adjust the Threshold (1) to a value that causes 3 dB gain reduction on the LED display next to the limiter section. Make sure that the attack control is all to the left.

VII) This gain reduction is possible with almost all common mixes and will not perturb anything. Turn the Treshold control one or two clicks to the left, to optimize the remaining control and figure out if a higher gain reduction is possible.

VIII) With more gain reduction you should get either audible pumping or low frequency distortion or both. Ignore the Low Frequency distortion for a while and optimize the Release setting (2). If no pumping is aubdilbe, move the release control to the right until you here pumping. Then turn to the left in small steps and find the longest possible setting without audible pumping.

IX) Check for low frequency distortion now. If there is any distortion, the only way out is to reduce the gain reduction. Readjust the Threshold control (1) until the distortion is not audible anymore.

X) use the Output Gain control (5) to adjust the output level to your needs

The U795 Stereo Mastering Limiter with Delay Line offers aditional functions to achieve higher gain reduction. Please click on the link for details.

Using the Limiter as additional compressor section.

If an external Limiter is used, the internal Limiter can be used as additional compressor section. It is best suited to add a tight compression for the high level range. The possible gain reduction is in the range of 4 to 6 dB. Start with a release time (2) of 0.3 sec and set the Attack control (3) to 3 msec. A Ratio setting (4) of 3 to 5 is appropriate.

Adjust the Threshold control (1) until you get about 6 dB gain reduction.

Optimize the release time - like describe in VIII).

Check for low frequency distortion. If there no distortion, you can either set the Threshold (1) to the left or the Ratio (4) to increase gain reduction. Find the setting, that offers maximum gain reduction, free from distortion. Check the release time setting (2) for pumping effects again.

Alter the Attack control and try to find a setting that causes an improvement. The sound will change in the range from approx. 1 ms to 6 ms, due to the different regulation of the transients.

Use the Output Gain control (5) to set an output level that meets your needs.

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Options:

Side Chain Equalizer for the Compressor Section
The U796 has a side chain insert that is activated by the S-C Ins Switch (16). It only affects the compressor section and leaves limiter and compressor unchanged. The W799 stereo side chain equalizer is best suited for this purpose.
Please, check for details here.

Control Ranges
We can adapt the control ranges to your needs. Please let us know what you are looking for here.

Inputs and Outputs
The module is available with electronically balanced and transformer balanced inputs and outputs.

Appearance
The colors of the faceplate, the control knobs, and switch caps can be determined by the customer.
Please, check for details here.

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FAQ's

What does Autogain do?

The autogain circuit calculates the gain reduction for any settings of the compressor threshold below 0 dBr. The calculation includes the settings of threshold, Ratio and Attack. It adds the result of the calculation to the output gain of the compressor. With short attack times, autogain is very precise (less than 0.5 dB error over the entire range). When using longer attack times, the peak output level depends on the transients that pass thru the compressor without causing regulation. It is not possible to calculate the output level with longer attack times precisely, since the influence of the structur of the audio signal is an unknown factor. Measuring the real voltage would be possible but result not in a static compensation of the gain reduction but an additional regulation. This is not what the autogain circuit is supposed to do. The correction with longer attack settings uses an empirically determined law, that results in an error between 0 and 3 dB over the entire range with common audio signals. During the setup phasee, the particular controls will only be changed in little steps, so the precision of the autogain is more than sufficient to keep the output level constant during that important phase..

Autogain does not consider any external side chain processing, and the settings of the Fill control and the Envelope control. With real-world settings, the influence of Fill and Envelope is low and will also not cause any disturbing differences. An external side chain EQ; however, can alter the gain reduction considerably. This cannot be be compensated by autogain anyway, since the autogain does not 'know' the eq setting, nor the spectrum of the audio signal.

The manual gain controls operate independent of the Autogain and are always available to compensate the any possibly remaining differences.

If you have any questions or comments, please let us know.

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