Summary Reverb fashions come and go and presently we seem to be in a phase of rediscovering reverb. However, I don't recommend that you drive the coil to the maximum, because it may shorten the life of the unit. He knows who he is, and that's the main thing. This installment of Foundations of Audio explains one of the most essential ingredients in audio mixing, reverb—the time it takes for sound to bounce, echo, and decay during a live performance or recording. However, computing power has continued to follow Moore's Law and today we have computers that would have been inconceivable back then. Normally two pickups, mounted at different positions on the plate's surface, were used to give a pseudo-stereo output from a mono input.
All changes up to 1. We also need to consider the maximum voltage needed to provide the required current into the coil at high frequencies. Nowadays, instead of trying to create a loud sound one sample in length which isn't very easy , impulse responses tend to be recorded using a sine wave swept over the whole audio frequency range over a period of a few seconds. While the spring worked well enough on vocals, guitars, and electronic organs, it wasn't so good on percussive sounds, as it had a tendency to 'twang' — the sound fluttered and pulsed as the reflections bounced back and forth along the length of the spring. It never sounds exactly like a room, but it certainly has a unique and interesting quality. Anything from 20ms to about 80ms will be the area you need to work in — beyond this you will create a distinctive slap back effect that could be cool in the right circumstances but less suitable for most. The meter is usually connected in parallel with the input to the drive amp, but there's no real reason that it can't be reconfigured to measure the signal level from the drive amplifier.
Typical tanks have two or three springs, which are usually slightly different to provide a richer, denser sound. Description The Spring Reverberation tile allows you to add the unique sound of a real spring reverb into a compact 1U space. One factor always to keep in mind when mixing is that a heavy application of reverb tends to make a sound appear to be more distant, and that's often at odds with the concept of a lead vocal that you want to keep upfront. The following table applies to the Type 4 tank - the 425mm long, 4-spring version as used by Fender and many others. This reduces the gain and provides the compression effect. As its name suggests, the plate reverb utilised a thin metal plate, which could be as large as one metre square or more, suspended in a soundproof box and driven into vibration by means of a transducer similar to the voice-coil assembly of a loudspeaker. Note that the value of R2 and R7 must be selected based on the coil impedance.
This can be helpful if the model number is missing or can't be read. Are there parasitic impedances, or electro mechanical effects that make the input impedance change in a way different than the simple math? Figure 5 - Basic Drive Circuit For Low Impedance Coil The circuit shown above requires that the input coil be isolated from the reverb tank chassis. In order to produce a constant drive level into a coil as the frequency varies, it is necessary to drive the coil with an amplifier that produces constant current, rather than the much more familiar constant voltage. This gives us the effect of a larger hall. The pickups share a common core similar to a transformer so their outputs are summed.
It's highly flexible, because there are many parameters to tweak. If you then use a computer to multiply this impulse response by every sample of new audio signal, the net result is that you add the original room's reverb to that audio signal. Fixes problems with line breaks in dialogs, and affects track meters. Used well, then, a touch of reverb here or there can add a completely new dimension to your mix. Springs and plates are mechanical systems that offer their own unique strongly flavored sort of resonance, and while their mechanical technology is hardly cutting edge--digital is the thing these days-- their sound is still relevant. Photo: Mark Ewing The way the plate works is that sound energy from the input transducer moves very quickly from the transducer near the centre of the plate to the edges of the plate, where it bounces back.
This took some of the harshness out of the spring and allowed me to turn it up louder. The reverb input signal can be continued to a separate output if desired. This is a piano clip with the preset applied. Initially digital reverbs came in rack form for studio recording or pedal form for guitarists. R7 is based on an estimation, where the resistor value is roughly 20 times the coil's 1kHz impedance. With 100nF as shown, the -3dB frequency is about 72Hz. The impedance was also verified using a vector impedance meter which gave virtually identical results.
Input Impedance Unlike driving a speaker, the drive signal to a reverb tank is ideally not flat, with respect to frequency. The Type 4 has been the unit of choice for many guitarists for a very long time, although some do prefer the other types. Figure 2 - Drive Transducer Details Above, you can see a close-up of the drive coil. Spring reverb Spring Reverb is an authentic spring reverb recreation that will add vintage character and grit to any audio track. Reverb chambers were also an option back in the 1950s which got to the heart of the reverb theory by simply capturing the sound of a room using speakers playing the music and microphones picking up the results of the music played in the room with all of its additional reverberation. I'd like to thank 'PhAbb' for suggesting the use of one of the el-cheapo 1k:8 ohm transformers to drive high impedance coils. The following table gives the suggested values for these resistors, based on the coil impedance.
In order to reproduce the build-up in complexity in the decaying reverb tail, multiple re-circulating filters usually a mixture of comb filters and all-pass filters were used, sometimes fed from the original input, sometimes from the outputs of the tapped delay line, depending on the designer. Figure 9 - Generalised Recovery Amplifier Circuit The circuit shows the basis for the recovery amp. C1 is chosen to provide the desired low frequency response. The larger the plate, the longer the reverb time — but these things were big, clumsy and heavy. Figure 11 - Clipping Indicator For Drive Level Monitoring It's a pretty simple circuit and will work well with the suggested opamp, which is cheap but has limited performance. The effect is identical to using a voltage amp with a series resistance. Despite the high operating voltage, this circuit will still struggle if you drive it a bit harder than normal.