Weak Joe Extreme Musical Compression

22 August 2003

Weak Joe Compressor Prototype The Weak Joe Photo-Optical Compressor User's Guide


Weak Joe is a stereo compressor/limiter intended for audio recording and mixdown. Its strength lies in its ability to sound musical whether used sparingly or driven hard.

Weak Joe uses a photo optical device to control the signal. This optoisolator consists of a light emitting diode coupled with a light dependent resistor. When a current flows through the LED the resistance in the LDR drops, causing a reduction in the level of the audio signal. The LED is driven by a side chain circuit that monitors the audio signal and varies the voltage to the LED based on that signal. A stronger signal therefore has the potential to allow a reduction in the output, creating signal compression.

Voltage controlled amplifier-based compressors such as those made by DBX have a linear, precise response in relation to the input. The light dependent resistor is an inherently non-linear device that has a more pleasing effect on most music sources compared to VCA devices.

Weak Joe has five panel mounted rotary controls per channel that allow you to adjust various parameters. From top to bottom they are: attack, release, threshold, ratio and gain. The first three affect the side chain while the last two directly affect the actual audio signal.There is also a front panel LED that displays the control voltage that is going to the LED inside the optoisolator. Note that although the LED on the front panel may be lighting up very brightly it is possible that the unit is having little or no effect on the signal. That is because the ratio knob can be set to 1:1, or no compression, and since it is connected to the audio part and not the side chain its effect or lack thereof will not be displayed by the LED. Think of the yellow LED as potential effect on the signal.

As the sole visual indicator of the compressor's operation the LED will provide valuable feedback of the ATTACK and RELEASE settings as well.

There are also three switches that provide true bypass for each channel and a link mode for stereo operation. More on that later.

The back panel contains three 1/4" jacks per channel that provide input, sidechain and output. There is also a 2.5mm jack for power. This should be provided by a 12 volt 1 amp ALTERNATING CURRENT adapter. Do NOT use an adapter that supplies DC - only an AC output of 10 to 25 volts will work. Also note that 9 volt AC adapters such as those used by many Alesis products will not supply sufficient operating voltage to properly drive the circuits in Weak Joe.

Internally, the Weak Joe uses NE5532 opamps in the audio path and TL072/LF353 devices in the sidechain. As the sidechain devices are outside the audio path their shortcomings are not introduced into the signal and are therefore of no relevance. That said, the performance of the TL072 is completely adequate for the task - in fact many well-regarded signal processors use TL072/74 devices within the audio path.

The 5532 has been around for over 20 years and has been used on large mixing boards and fine audio equipment alike. Though there have been many attempts it has yet to be beaten on specifications by more modern devices. It is something like a piece of vintage audio equipment still being manufactured.

It would be difficult to find a more pristine signal path in a compressor. Even at high compression setting you can expect Weak Joe to add little noise or distortion to the signal.

Hooking Up Weak Joe:

Connect power to the power jack and note that the green power light on the front panel is glowing. Turn all contols to the extreme counter-clockwise position.

Compressors are ordinarily connected to the channel inserts of your mixing board. There are two ways to connect Weak Joe to a channel insert. The simplest way is to use a stereo 1/4" to stereo 1/4" plug. Plug one end into the channel insert of the board and the other to the input of Weak Joe. The return signal will be sent to the ring of the stereo plug back to the mixing board. No additional output connection is required.

The other way to hook Weak Joe to a channel insert is to use a stereo 1/4" to two mono 1/4" Y cord. The tip signal goes to the input of Weak Joe and the ring-connected return plug is connected to the output.

You can also use Weak Joe as an inline effect on any line level signal. Just hook the input to the signal source and the output to an amplifier, mixer input or other device.

Basic Operation:

Check that the bypass switch is in the off position (the switch is placed so that it interferes with the setting of the gain control when switched 'on' to provide a tactile cue). With a signal going through Weak Joe turn the THRESHOLD knob until you see the yellow LED illuminating with the signal. Rotate the RATIO knob until you can hear the effect of the control voltage on the signal. Change the ATTACK and RELEASE setting to suit the type of input. Alter the gain until the perceived loudness matches the input (check it against the unprocessed signal with the bypass switch).

Note that at the higher RATIO settings Weak Joe can provide negative gain meaning that a loud signal can actually become quieter than a soft one. Note also that there is some degree of interaction between the THRESHOLD and RATIO controls even though they are electrically isolated. Because there are no definite markings for each knob position you are essentially forced to use your ears to set up the compressor. In time you'll find this is much more satisfactory than saying "electric bass needs a 1:4 compression at -15 dB threshold" or "female vocals need a 1:2 compression with a 50ms attack and a 500ms release".

Modes of Operation:

Weak Joe contains two identical compressors which can be used in various modes:

  • Dual Mono (Independent)
  • Stereo Linked
  • Chained
The first mode is independent where two completely different audio signals can be fed to each compressor with no interaction between them at all. You could use this mode for compressing a vocal track in one channel and a snare drum in the other. Each signal would be treated completely seperately from the other.

The next mode is stereo linked where the control voltage is applied equally between the two compressors. This mode is used when you are feeding a stereo signal into your Weak Joe and prevent the stereo image from 'wandering' between the two speakers. When a strong signal comes into one or the other channel it affects the level of both channels. The strongest signal is used to control the gain stage.

Weak Joe can also be used in the chain mode where the first compressor's signal is fed directly into the second one. Using a patch cord between the two channels, different characteristics can be set on each channel creating a smoother effect on certain source material.

When using the stereo linked mode, start with similar parameters set on each channel. Even though the two channels are 'linked' the sidechain of each channel still performs independently of the other. If, for example, you have set a long release time in the right channel and a shorter one on the left a strong signal coming into the right channel will result in a longer release time for both channels while a transient in the left will create a short release time for both channels. There may be times when this is exactly the effect you are after but generally you should start with the same setting on each stereo channel including threshold and ratio settings. This will ensure the closest possible tracking between the channels.

Using the Sidechain:

The sidechain jack accepts a TRS 1/4" 'stereo' plug. Similar to a channel insert, the sidechain jack sends the buffered input to the tip of the TRS and accepts a signal from the ring which, in turn, goes to the first stage of the sidechain. In this way a signal other than the compressor input can be used to control the compression of the input signal.

One commonly given example of using the sidechain is putting the bass track through the input and feeding the sidechain from the kick drum. This is supposed to be a good way to tighten up sloppy bass tracks. Suggestion: if you need to use this technique you should think about getting a new bass player instead.

Perhaps the most recognized use of the sidechain is to turn your compressor into a 'ducker'. We're all familiar with the background music reducing in volume each time the radio announcer speaks. Feed the background music into the compressor inputs and a split from the announcer's voice into the sidechain input.