I and Albin talked about what JFet’s can be used for in a possible musical kit and one property of J fets is that they can be used as variable resistors with applications such as Compressors,Constant Volume Circuits. Limiters, Voltage Controlled Filters,Tremolo et.c.

Now the resitive range of a J Fet is limited while it can be enhanced with linerization feedback. Designs that have wide range usually require matched devices and advanced linerization to achieve range of 80dB but the circutry needed for that is far bigger than a guitar pedal 

and so looking at musical applications, a common one is that of a ’Talent Booster’ a sort of mild compression that just equalizes small dips in response to make playing more fluent.

 

Typical applications for compression

Compression is used in studios and radiobroadcasting in the latter often a series of up to 12 compressors set very mildly and this is why records always sound bigger on radio than they do on stereo. Compression is used to decrease the dynamic range of instruments and for electric guitar the dynamic range is about 80dB

 or 10000 times between the weakest and the strongest. Typical dynamic range of a cassete player is a mere 35dB for small ones to 50dB. A plucked note on an electric guitar results in a transient that is 20dB ( 10 times) higher than the mean value of the decayed note and this gives the guitar it’s caracteristic sound.

As a comparison a pålayed not on an organ has no transient but the note swells to final value. Musically the transient of a guitar is often used to set rythm of songs. Now having 80dB dynamic range  is a bit awkward and makes transients very sharp or weak parts unheard and so musicians tend to like a dynamic range much smaller

40dB (100 times) to 6dB ( 2 times) or even less: heavy distortion or fuzz can diminish dynamic range to as low as 3dB and then all notes are at equal volume and you can precisely hear a difference between the weakest note and the strongest.

However in an expriment I made at NAMM with 35 musicians including one vilonist where I asked them to play the loudest note they were going to use and I set onset of distortion right there and then asked them to play and later asked them if they felt comfortable with the dynamic range and all were.

The dynamic range was then typically reduced to 20dB to 40dB meaning you still had the transient but the following decay would be louder than normal and of course that works like a ’talent booster’

Of course modern CD and home music theaters can allow dynamic ranges up to 120dB but let’s look at human hearing and then what cause hearing damages is sudden transients. Human hearing is frequency dependent and volume dependent in that at low levels the ear hears mostly around most sensitive area at 1KHz and because of this 

early HiFi goit ”loudness” compensation that increased bass and treble and then often to follow the setting of the volume control. As sound levels increase the human ear eventauilly reaches a maximum and starts to compress mainly around most sensitive area ( 1KHz) but bass and treble can increase in volume: this is why sounds set for high volumes usually are more midrangy than sounds set at low levels and also why at low levels a sound that is slightly louder or more trebly is percieved as better. Eventually the human ear reaches a point where all frequencies are compressed. The huma ear can do this dynamically but is slow in response and so sudden transients can cause hearing damages. This explains why people can listen to loud concerts without hearing damages but that sudden increases in volume such as explosions or jet engines starting can give hearing damages. A beautiful thing is that the human ear can recover but only if left to heal.

One can then argue if a dynamic range of an electric guitar ( or any musical instrument) is better at 80dB dynamic range than at 40dB?

Interestingly humans do not only hear with the ears but also absorbs sound as vibrations. This is why  sound is said to be better at high volumes. One can argue at what sound level is music most enchanting? Possibly that also depends on type of music.

However this above hints why mild compression can work as a talent booster and also make the played music more comfortable and in every day playing the diminishing of dynamic range making for more comfortable playing.

 

 

 

The J Fet compressor kit has a mild compression and when set as intended with the trimmer there is no ducking at transients but weak parts of the decay are amplified

 

A studio rule of compression is set compression level so you cannot hear that it is on but miss it when it is off. Obviously there are many famous recordings using ’over compression’ so that transients give a clipped sound.

Further on compression use in studios, sometimes even on distorted guitars it can be useful to add a small amount of compression and partly affects the musician with a feeling of playing louder but it can also make the recorded guitar track easier to mix so that no weak parts are lost.

 

There are a number of technical points of interest with this circuit in terms of amplifier techniques to some extent explaind in the product text

 

 

Have fun

Bjorn