AF’s Weblog

July 28, 2011

Mysteries of Dynamics Processing Revealed

Filed under: Compressors, Processors, Recording reviews — Tags: , , , , , — audiofanzine @ 7:34 pm

A dynamic processor is something that outputs a signal, where the level of the outgoing signal is based on the level of the incoming signal. In other words, a loud signal coming in will come out differently than a quiet signal coming in.

Basic types of Dynamic Processors

Compressors: The most common – the louder the signal is coming in, the less level it provides going out. In a compressor, a target level is set – called the “threshold” – and any signal coming in that exceeds that level will be reduced. The higher the level is above that threshold, the more reduction will occur. More on this later.

 

Limiters: Limiters are like super compressors. The idea is to ensure that the level does not exceed the threshold. Because this amount of compression is extreme, a limiter relies on certain functions and design that regular compressors do not have.

Expanders: The quieter the signal is coming in, the less level it provides going out. In other words – it makes quiet signals even quieter. Much like a compressor, the threshold is set at a certain level. Any signal that does NOT exceed that threshold is reduced, and the quieter the signal, the more reduction is done.

 

Gates: Gates are like super expanders. Anything that does not exceed the threshold is reduced to inaudible. Again, because gates are extreme, they often require a slightly different design than a regular expander.

 

Now – I’ll focus primarily on Compression, because that’s going to be the most commonly used dynamic processor.

Compression

Every signal you hear is compressed??? Yes, every signal you hear is compressed.

Bare with me. Imagine you have a rapper in front of a microphone. The rapper raps, you record. You play it back. You haven’t used any processing – you’re just playing back the raw vocals.  You are listening to a signal that has gone through at bare minimum 3 stages of compression – and more likely than not – closer to 6.

  • The microphone capsule gains tension as the rappers voice pushes it – in other words – it pushes back. The more the rapper’s voice pushes in – the harder the capsule diaphragm pushes back. In other words, the louder the signal is hitting the capsule, the more reduction the capsule does to the signal. That’s compression! (It’s mild compression, but it’s still compression).
  • Along the way through the microphone, you may hit a tube. Tubes have a non-linear response to voltage – the response is quite curved, and also changes the frequency balance of the signal. This is called saturation – which will tend to “round out” a signal, by reducing the loudest peaks. Compression! And before leaving the microphone, the signal may hit a transformer as well, which will saturate in a similar way… more compression.
  • The preamp is going to have multiple stages of saturation – and often times, the more gain you give something – the deeper that saturation curve goes. In other words, the more you drive the signal at the preamp, the more compression the signal experiences.
  • Then the sound has to actually come out of the speaker cones. Well, those speaker cones are going to build up tension when pushed further. See where this is going? This is called “cone compression”.

Ok – so this is a bit of a simplification – but there’s a point here. The point is that “compression” is always part of the signal. Some mics have less of it, some have more – same with speakers, tubes, transformers, etc. And they all do it in different ways. With tubes, people will talk about their saturation curves and %THD (total harmonic distortion – or frequency alterations). With mics, people will refer to how it “grabs” a sound – or more specifically – the sound’s shape.

Now let’s take a closer look…

Maximum Punch

There is a thin line between a transient sound, and a sustained sound. A sound that holds for any noticeable amount of time is sustaining. A sound that moves by too quickly to register as it’s own moment is transient. But transients can vary in length. A transient can be half a millisecond or it could also be ten milliseconds; they won’t sound the same. A big factor in punch is how long that transient exists. A quick transient sounds “spikey” – but a long transient sounds “punchy.” You want to find the point that makes the transient exist as long as possible before “flattening out” or becoming a sustained sound. Only your ear can tell you where that point is.

 

Good samples are already shaped to have that kind of impact – and any additional compression may actually soften that. Of course, punch has a lot to do with frequency as well – but that’s for another article.

 

Now what about the release? The release is super elusive. It determines how long it takes for the compressor to let go. If the release is too short for the signal you are going to get a disjointed sounding shape which usually results in distortion. If it’s too long, your signal never really returns to its natural shape, and you generally lose tone (or you just get permanent drive on the compressor’s output, giving the whole signal a new bit of tone). So the idea is to find a point that emphasizes the sustain (which is where most of the signals tone lives) properly.

 

Lastly, when the attack and release are set in a way that seem to argue – the compression can become very audible. You either hear the decent or the ascent of the signal level. This is called pumping. It’s generally annoying, but can sometimes be used an effect. If audibly desired, consider the rhythm of the release time, and ask yourself if it’s groove is complimenting the song.

———————————-

So, rather than thinking of a compressor as something that effects the “level” of a signal. Think of a compressor as something that effects shape. Why? Because level can be controlled with the volume fader more accurately and transparently. A fader doesn’t really control shape, unless you are being extremely meticulous. Conversely, compression will always effect the shape of the sound it is working on.

Once you start hearing shape, you will understand compression.

To read the full detailed article see:  Mysteries of Dynamics Processing Revealed

Advertisements

March 4, 2011

Noise Gates Don’t Have to be Boring

Noise gates aren’t as relevant as they were back in the analog days, when hiss was an uninvited intruder on anything you recorded. But noise gates can do some really cool special effects that have nothing to do with reducing hiss. This article shows how to make them a lot more interesting, and throws in a bunch of fun audio examples, too. But first, let’s do some noise gate basics for the uninitiated.

Noise Gates Basics

A noise gate mutes its output with low-level input signals, but higher-level signals can pass through. Following are the typical adjustable parameters found in a noise gate, whether analog, digital, or plug-in.

  • Threshold: If the input level to the gate passes below the threshold, the gate “closes” and mutes the output. Once the signal exceeds the threshold, the gate opens again.
  • Attack: This determines how long it takes for the gate to go from full off to full on once the input exceeds the threshold.
  • Decay: This sets the time required for the gate to go from full on to full off once the signal falls below the threshold. Since decaying signals often criss-cross the threshold as they decay, increasing the decay time prevents “chattering.”
  • Key input: Normally, the gate opens and closes based on the input signal’s amplitude. The key input allows patching in a different control signal for the gating action (for example, using a kick drum as the key signal to turn a sound on and off in time with the kick’s rhythm). Note that in most cases, you won’t find this in plug-ins, only in hardware units.

All right, let’s get into applications.

Selective Reverb

I was using a premixed drum loop from the Discrete Drums Series 2 library, but in one particular part of the song, I wished that the snare—and only the snare—had some reverb. Although Series 2 is a multitrack library, I didn’t want to go back and build up the drum loop from scratch. So why not just extract the snare drum sound, put some reverb on that, and mix it in with the drums?

Referring to Fig. 1, I copied the drum loop in Track 1 to a second track in my sequencer (if you were doing this in hardware, you’d split it into two mixer channel inputs). In the second track, there’s EQ inserted to roll off all the low end, which took most of the kick out of the signal, as well as the high end, to reduce the level of cymbal crashes.

Reverb sélective

Fig.1

The next step was to insert a noise gate in Track 2, and raise the gate threshold so that only the snare peaks made it through (the screen shot shows a Compressor/Gate plug-in, but the compressor was disabled by setting the ratio to 1:1). These peaks fed the reverb, which dumped into the master bus along with the original drums. The end result: Reverb on the snare only, added in with the rest of the drums.

Now let’s take a closer look and listen to some samples…

Kick Drum “Hum Drum”

Here’s a trick for hardware noise gates. Suppose you want to augment an existing kick drum sound with a monster rap kick, like that famous TR-808 rap sound. Here’s a sneaky way to do it:

  1. Set a sine wave test tone oscillator somewhere between 40 and 60Hz, and plug it into a mixer channel module containing the noise gate.
  2. Patch the kick drum into the gate’s key input and set the threshold relatively high, so that the kick exceeds the threshold for only a very short amount of time.
  3. Set the noise gate decay for the desired amount of oscillator decay. Hopefully your gate decay can go up to about 2 seconds, but even 1 second can do the job.

Now whenever the kick drum hits, it opens up the gate for a fraction of a second and lets through the sine wave; the decay time then provides the desired fadeout.

Real Time Manipulation

This real-time performance tip can sound very cool with hip-hop, techno, and other types of music that rely on variations within drum loops. With most loops, the snare and kick will reach the highest levels, with (typically) hi-hat below that and percussion (maracas, shakers, tambourine, etc.) mixed in the background. Tweaking the noise gate threshold in real time causes selected parts of the loop to drop out. For example, with the threshold at minimum, you hear the entire loop. Move the threshold up, and the percussion disappears. Move it up further, and the high-hat drops out. Raise it even higher, and the snare and kick lose their decays and become ultra-percussive.

To read the full detailed article with sound samples see: Noise Gates

 

February 9, 2009

NAMM 2009: Video Demo True Systems P-Solo Ribbon

Presentation of the new P-Solo Ribbon preamp for ribbon and dynamic microphones from True Systems.

To watch all NAMM 2009 video demos visit us on Audiofanzine NAMM 2009.

Create a free website or blog at WordPress.com.