As we stated last month, stereophonic sound is the reproduction of music using two speakers to create a soundstage or stereo image, a process called stereophony. In 1949, Helmut Haas wrote his Ph.D. thesis about a phenomenon which has since become known as the Haas effect.
This effect is the ability of the human brain to perceive the location of a sound based on the time of arrival at each ear. Humans will perceive the direction of sound as the direction of the ear where the sound arrives first by up to about 25 ms, even if the later arriving sound is louder by as much as 10 dB. If the second sound arrives later than 25 ms, it is heard as two distinct sounds.
A similar effect, called the law of first wavefront was described by Lothar Cremer in 1948. Hans Wallach and others reported the effect in 1949 which they called the precedence effect. A related effect is sensory inhibition, the phenomenon in which a response to one stimulus causes the response to a second stimulus to be inhibited. For example, a sound entering one ear causes us not to hear a sound entering the other ear when it is delayed by less than 35 ms.
These effects are what make stereophonic sound possible. Last month we talked about interaural time difference (ITD), which is the human brain detecting the direction of sound due to the difference in arrival times for the two ears. That perception allows for time-difference stereo, using two microphones spaced at some distance apart so that time of arrival provides the primary stereo information. It is also called time-of-arrival stereo or difference-in-time stereo.
Last month we also mentioned interaural level difference (ILD) in which direction is determined by the difference in sound intensity between the two ears. That allows for intensity stereo when the stereo image produced by the difference in level between the left and right channels. In fact, two microphones placed at the same point, but angled in different directions can produce a stereo image because of this effect.
Both of these effects help to create true stereo, recordings made with two or three microphones rather than panpot stereo, which is manipulated by the mixing engineer.
What about the sound that seems to come from between the two speakers? That phenomenon, called a phantom channel or phantom center, occurs because the sound arrives at both ears at the same time, with the same intensity, and in phase. When the same effect occurs with a surround sound system, it is known as a phantom image.
Just to round out this subject, we have the terms diotic and dichotic. Diotic is when you have an identical sound in both ears. The opposite is dichotic, when there are different sounds in each ear.
• On September 11, 1977, David Bowie and Bing Crosby, pop stars from two different generations, came together to videotape "The Little Drummer Boy" for a Christmas TV special to be aired two months later. The recording was made in just three takes. A month later Bing Crosby died on October 14, having never seen the video.
• After he sobered up in 1989, Ringo Starr sued to stop the release of an album that he had recorded while he was drinking, claiming he sounded too drunk. The court agreed and the album was never released.
• Three Dog Night had a No. 1 hit in 1972 called "Black and White." It was originally written in 1954 by David I. Arkin and Earl Robinson about the US Supreme Court decision Brown v. Board of Education, which prohibited racial segregation in public schools. The original lyrics of the song opened with this verse:
Their robes were black, Their heads were white,
The schoolhouse doors were closed so tight,
Nine judges all set down their names,
To end the years and years of shame.
In the Studio
A few years ago, we had young man come in as a session player to play on several songs we were tracking. He played lead guitar and fiddle—as mean a fiddle as I've heard anywhere. His name was Levi Darr. At the time he was living in Luckenback, Texas, and played regularly at some of their picking cirlces.
Today he makes his home in Boerne with his wife Faith and their son. He has recorded one solo album and several cuts from that album can be seen on YouTube. He returned recently from a European tour, where he played guitar and fiddle with Kim Carson and the Enablers from New Orleans. Currently he plays regularly at various clubs and restaurants around the Texas Hill Country, playing with Gary Michael Jones, T. Roy Miller, and others.
Free Studio Time
Want to receive some free recording time in the studio? If you refer someone to Los Senderos Studio and they come in for a recording session, I will give you two free hours of recording time. That's a $50 value. Simply send the name of your referal on an email. As soon as they come in to record, I will credit you with a two-hour session. What could be easier?