Even when we are outdoors, a significant amount of sonic energy is reflected back to the ears by the ground and nearby structures – even by surrounding vegetation.
We only begin to notice these reflections when the time delay is more than about 30 milliseconds to 50 milliseconds, in which case we become consciously aware of them as individual sounds and call them echoes.
Special rooms called anechoic chambers are built as research rooms to absorb reflected sound energy. In a test situation staged in an anechoic chamber, only the directly radiated sound energy reaches the ears.
Upon entering an anechoic chamber for the first time, most people are astonished by how much softer and duller any sound source sounds. If reflected sound is so common in an ordinary acoustic environment, I’ve always wondered why these reflections don’t interfere with our ability to localize sound sources.
I guess it’s because our binaural hearing sense can quickly adapt to a new acoustic environment. I do know that our hearing system uses only partially understood mechanisms to suppress the effects of reflections and reverberation.
The fact that we localize sound sources on the basis of which signals reach our ears first is known as the precedence effect. This is not to say that we are unaware of the reflections that follow. Actually, we subconsciously use the subsequent reflections to estimate range, or the distance we are from the sound source. In my opinion, a music producer/engineer is no better than his tools.
Our main tools are, of course, a good pair of ears and the wonderful brain to which the ears are connected. If the hearing is faulty, only faulty judgments can result. Please try to remember that good hearing is a rare and wonderful gift.
How Do We Achieve Depth, Or That Third Dimension, In A Stereo Image?
The feeling of depth perception in a recording is the result of a combination of values, including the ratio of direct to reverberant sound. The intensity of a sound source relative to others in the same field, and even EQ, especially in the presence area of about 1.5 kHz to, say, 5 kHz.
Probably the most important factor in creating a feeling of depth is the change in the ratio of direct to reverberant sound. As reverberant energy becomes more prominent, the source appears to move back.
The absence of early reflections in a sound source makes it seem much closer. As you change the quality of early reflections in a soundfield, they greatly affect the depth of field. These reflections are generally less than 40 milliseconds.
When they are longer than that, the ear can pick them out as individual reflections, but below 40 milliseconds they tend to smear into one sound. Early reflections in a sound source must be part of the sound-field of the original recording to be effective. There are virtually no effects devices that seriously address this important issue!
Thinking out and carefully designing a sound-field yields big benefits. Careful thought and intent will make your work memorable and separate you from the also-rans.
That is also why intelligent use of pre-delay with reverb devices can give a tremendous feeling of depth of field. By increasing the length of the pre-delay of a reverb device (to make sure the reverb itself does not cover the early reflections), your recording will have a unique sonic character that is truly your own.
The Attack Wall
Here’s something about “tube traps” that you may find interesting. I am very excited about a new and intriguing recording-room acoustical treatment.
In essence, this new theory creates a reflection-free listening zone for music recording and mixing. The concept was perfected by my friend Arthur Noxon of Acoustic Sciences Corporation.
The “attack wall” at Westviking Studio. (click to enlarge)
It’s called the “attack wall.” It is a free-standing wall that surrounds the monitor speakers. (I think we could call this speaker position “midfield” monitoring.) It acoustically loads the monitor speakers, and causes them to play as if there actually mounted into a wall. This gives the monitor speakers increased acoustic efficiency.
With an array of studio traps behind the listening space, the “attack wall” makes a 100 percent acoustically “dead” space. This creates a reflection-free zone for music mixing and recording.
I have found that with the “attack wall,” no monitor EQ is necessary.
With good monitor speakers, you hear smooth, linear sound. The low end is exceptionally clean and articulate. One of the additional advantages of the “attack wall” is its portability. It can be moved from place to place with a great deal of predictability and reliability.
In my next article, I’ll be discussing speakers, amplifiers, control room volume levels and much more.
Click to enlarge book cover
This is an excerpt from Bruce Swedien’s Make Mine Music. To acquire a copy of this book, click over to www.musicdispatch.com. NOTE: ProSoundWeb readers can enter promotional code NY9 when checking out to receive an additional 20% off the retail price plus free shipping (offer valid to U.S. residents, applies only to media mail shipping, additional charges may apply for expedited mailing services).