AF’s Weblog

October 14, 2009

Basics of Acoustics: Time (I)

Filed under: Instructional articles — Tags: , , , , , — audiofanzine @ 6:01 am

Time (1)

With stopwatch in hand, our perception of time seems straightforward. But in everyday life we’re not always watching the clock, and everyone knows that the passage of time is relative. It differs from one person to another and especially from one activity to another: An hour spent watching a great movie doesn’t feel as long as an hour in traffic.

SignalFig.1a : Sound signal with reverb. Note the progressive attenuation of the sound level

Scientists may conceive time in seconds, but most musicians feel it in a more fluctuating manner: either in the speeding up of a tempo or the slightly off-pitch note due to stress. In fact, pitch, which is defined by frequency, is a value linked to time and depends on our perception of a second. If it seems longer or shorter, the note can seem sharp or flat.

It’s said that during the middle ages, long before the invention of the metronome in 1816, a person’s pulse was used as the reference. It was therefore better to choose a musician who was calm.

Signal reverseFig.1b : The same signal, through a reverse effect Reverse : maximum gain is at the end of the signal

An Experiment

For those of you who can remember magnetic tape, a piano note played in reverse doesn’t sound at all like a piano, and a verse of Shakespeare in reverse sounds strangely like…Swedish. In fact, what our ears perceive as a single homogenous sound is really like a small train made up of four different cars: if we watch it as it moves forwards or backwards, the order of arrival won’t be the same and therefore our perception of the sound will be different.

It’s this idea that’s expressed through the notion of the A.D.S.R curve, also called envelope curve. A « reverse » preset found on some reverbs manipulates nothing but the reverb envelope. It will probably be a decreasing sound and look like figure 1. If it’s played in reverse, the end will therefore be played before the beginning (figure 1b).

Compression

The second case in which a musician-technician might find themselves confronted with having to manipulate an envelope generator: a compressor. A compressor usually has envelope adjustments that change the action time of the compression effect (fig. 5)

Depending on the gear, you’ll usually find an Attack adjustment, which corresponds to the time the compression kicks in once the signal reaches the limit of compression. By putting this setting on slow, the compression will be much more discrete and lets you assure a certain amount of compression without it being too sensitive (for classical music for example). But on the other hand, all sudden peaks corresponding to short attacks will escape treatment. A short Attack adjustment will allow the compressor to react instantly , but that typical compressed « punchy » sound will be heard. In today’s music this can be a desired and interesting effect, if used with moderation. You can also modify the Release which adjusts the time it takes the compressor to bring the level back to its initial level. As with the attack settings, a middle setting will be more discrete and will be more delicate in bringing the level back down. The opposite, a release set to zero can, if the compressor intervenes often, give a disagreeable wave effect.

Figure 5Fig 5a: Cubase’s standard compressor

Figure 5Fig 5b: TC Electronics TC CL1B plug-in which models a tube compressor

To read the full detailed article see:  Basics of Acoustics: Time

Advertisements

September 30, 2009

Understanding Reverb

When we hear sounds in the “real world,” they are in an acoustic space. For example, suppose you are playing acoustic guitar in your living room. You hear not only the guitar’s sound, but because the guitar generates sound waves, they bounce off walls, the ceiling, and the floor. Some of these sound waves return to your ears, which due to their travel through the air, will be somewhat delayed compared to the direct sound of the guitar.

This resulting sound from all these reflections is extremely complex and called reverberation. As the sound waves bounce off objects, they lose energy and their level and tone changes. If a sound wave hits a pillow or curtain, it will be absorbed more than if it hits a hard surface. High frequencies tend to be absorbed more easily than lower frequencies, so the longer a sound wave travels around, the “duller” its sound. This is called damping. As another example, a concert hall filled with people will sound different than if the hall is empty, because the people (and their clothing) will absorb sound.

Reverberation is important because it gives a sense of space. For live recordings, there are often two or more mics set up to pick up the room sound, which can be mixed in with the instrument sounds. In recording studios, some have “live” rooms that allow lots of reflections, while others have “dead” rooms which have been acoustically treated to reduce reflections to a minimum – or “live/dead” rooms which may have sound absorbing materials at one end, and hard surfaces at the other. Drummers often prefer to record in large, live rooms so there are lots of natural reflections; vocalists frequently record in dead rooms, like vocal booths, then add artificial reverb during mixdown to create a sense of acoustic space.

Whether generated naturally or artificially, reverb has become an essential part of today’s recordings. This article covers artificial reverb – what it offers, and how it works. A companion article covers tips and tricks on how to make the best use of reverb.

Now let’s take a sneak peak into the nitty gritty of reverb…

….

Advanced Parameters II

High and low frequency attenuation. These parameters restrict the frequencies going into the reverb. If your reverb sounds metallic, try reducing the highs starting at 4 – 8kHz. Note that many of the great-sounding plate reverbs didn’t have much response above 5 kHz, so don’t worry if your reverb doesn’t provide a high frequency brilliance – it’s not crucial.

Reducing low frequencies going into reverb reduces muddiness; try attenuating from 100 – 200Hz on down.

Early reflections diffusion (sometimes just called diffusion). Increasing diffusion pushes the early reflections closer together, which thickens the sound. Reducing diffusion produces a sound that tends more toward individual echoes than a wash of sound. For vocals or sustained keyboard sounds (organ, synth), reduced diffusion can give a beautiful reverberant effect that doesn’t overpower the source sound. On the other hand, percussive instruments like drums work better with more diffusion, so there’s a smooth, even decay instead of what can sound like marbles bouncing on a steel plate (at least with inexpensive reverbs). You’ll hear the difference in the following two audio examples.

Maximum DiffusionNo Diffusion

The reverb tail itself may have a separate diffusion control (the same general guidelines apply about setting this), or both diffusion parameters may be combined into a single control.

Early reflections predelay. It takes a few milliseconds before sounds hit the room surfaces and start to produce reflections. This parameter, usually variable from 0 to around 100ms, simulates this effect. Increase the parameter’s duration to give the feeling of a bigger space; for example, if you’ve dialed in a large room size, you’ll probably want to add a reasonable amount of pre-delay as well.

Reverb density. Lower densities give more space between the reverb’s first reflection and subsequent reflections. Higher densities place these closer together. Generally, I prefer higher densities on percussive content, and lower densities for vocals and sustained sounds.

Early reflections level. This sets the early reflections level compared to the overall reverb decay; balance them so that the early reflections are neither obvious, discrete echoes, nor masked by the decay. Lowering the early reflections level also places the listener further back in the hall, and more toward the middle.

High frequency decay and low frequency decay. Some reverbs have separate decay times for high and low frequencies. These frequencies may be fixed, or there may be an additional crossover parameter that sets the dividing line between low and high frequencies.

These controls have a huge effect on the overall reverb character. Increasing the low frequency decay creates a bigger, more “massive” sound. Increasing high frequency decay gives a more “ethereal” type of effect. With few exceptions this is not the way sound works in nature, but it can sound very good on vocals as it adds more reverb to sibilants and fricatives, while minimizing reverb on plosives and lower vocal ranges. This avoids a “muddy” reverberation effect that doesn’t compete with the vocals.

THE NEXT STEP: APPLYING REVERB

Now that we know how reverb works, we can think about how to apply it to our music – but that requires its own article! So, see the article “Applying Reverb” for more information.

To read the full detailed article see:  Understanding Reverb

May 23, 2009

Making a Studio Pt.3

Making a Studio Pt.3
Acoustics

Sound is a wave, much like the ripples on a still body of water when a rock is dropped into it. The larger the wave, the lower the tone. Lower tones, known as bass frequencies, travel in wide long waves while higher tones known as treble frequencies travel in a tighter, shorter wave. Frequencies heard by the human ear range from 20Hz to 20K. Just as an indication, a piano’s range, probably the widest range of any instrument, is from 39Hz on the low note and 3Khz on the high note.

Plan de groupe A typical 1/3 octave graphic EQ plugin with frequencies ranging from 20HZ to 20K

Sound is measured in decibels also represented as dB. An average concert is about 95-100 dB while a heavy rock concert or hip hop concert could reach levels of 130dB. This is above the threshold of pain; so don’t forget to wear your earplugs which are designed to protect your hearing when in extreme sound levels. Interestingly enough, whales can actually produce levels of up to 180dB. It should be remembered that taking care of your ears is the most important thing you can do to prevent damage and have a sustained career. So don’t hang out with any whales and put some protection in your ears when exposed to loud volumes.

Plan de groupe A typical 1/3 octave EQ spectrum analyzer with frequencies ranging from 20HZ to 20K

Now let’s take a closer look at other aspects…

Commercial & Private Studios

The commercial studio is there to provide the ultimate service for anyone who wants to pay. They are out to cater to the demanding Artist. The ultimate goal for the commercial studio is to make a profit. Top recording artists have healthy budgets to get that ultimate sound. Many artists like the no hassle style of recording that the commercial facility provides. The premier studios will have all the requirements needed to have a smooth production.

Plan de groupeCherokee Studios [1]

The studio equipment is always the latest and most technologically advanced to keep up with the never-ending race for the most groundbreaking sound creation device. Commercial studios are constantly purchasing new gear. The elite studios will also have a collection of vintage gear as well. Vintage gear has a certain character that can only be reproduced by the older technology. This becomes a very valuable asset in achieving alternative sounds.

The studio staff is available for what ever any artist, engineer, or producer may need. High-end full service studios can accommodate any possible situation from a simple rock band to a huge orchestral string section.Most studios have interns or runners that are required to do anything asked of them. At any given studio the interns may be seen washing cars and cutting grass.

The assistant engineer in most cases will have immense knowledge of how the room is setup and be able to quickly reply to any request that is commanded. He becomes the engineers’ right hand for connecting all the microphones and patching outboard gear. The Assistant Engineers’ job is basically limitless. Knowing how to make a good cup o’ coffee can definitely come in handy. Sessions can literally go for days at a time, and the commercial studios are setup and accustomed to the long hours. The technicians are on staff immediately if there is a problem with anything breaking down. Studio gear is very sensitive and delicate, therefore is does breakdown often. Many times user error may cause gear to be not working at times and if the Assistant can’t figure out the issue then a Tech will surely be able to troubleshoot the problem.

Upscale studios will also have security and respect for privacy for sensitive productions. Even getting into some studios without an appointment could be like getting into Fort Knox. All great studios will also have reliable recommendations for musicians, engineers and producers if they are not already on staff.

Plan de groupeVillage Studios [2]

What to look for

Look for studios that have recorded records that are similar to the Artist you are recording. Simply pick up the records you like and see where they where recorded and by who they were recorded. You will be surprised that you will see many names recurring. Check the discography of the studio to see how much experience the studio has. If many hits were recorded there it is a good sign that the studio is doing its job. That is one of the best references a studio can have. The Engineer should be consulted to make sure that all the proper equipment; software and microphone selection is available for the style of music that is being recorded.

If everything is clean and in working order that signifies that the studio will also take pride in your music. Quickly overlooking that all the lights are in working condition on the gear and console is a simple way to see that the equipment is properly maintained. Changing light bulbs is a simple task. If that is taken care of, that is also a sign that the studio is on top of their maintenance. Polite and professional atmosphere is of up most importance to the entire process. Nobody wants to deal with attitudes. Remember the Artist is the only star that shines in his booked studio time. Seeking a studio that has the vibe or atmosphere that makes the Artist or Producer comfortable is a key issue in determining where to establish the recording process also. Many hours will be spent within close quarters so décor and general atmosphere is a main concern.

The Private Studio

Many Producers and engineers have their own private studio. It is common nowadays that the recording budget is spent on purchasing gear for a studio. The benefit is that the equipment belongs to you in the end. Another major advantage is that you will not be charged by the hour for studio time. Average studio rates are from $50 to $250 per hour.

Privacy and secrecy is much more controlled in a private studio as well.

Privacy and Setting the Mood

Keeping all sessions under a vale of secrecy is highly important. New music is constantly being recorded in every studio. It is imperative that this music does not fall into the wrong hands. If it leaks out into the public before it hits the airwaves it could lose momentum for a successful single. Even worse the possibility of another artist stealing the song may be a factor without sufficient security and privacy.

To read the full detailed article see: Making a Studio Part 3


Blog at WordPress.com.