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Smokin' TomGary
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| Posted: 11 February 2017 at 7:23pm | IP Logged
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In the Hard To Find 45's On CD, vol 17 thread a reference is made to how a song would have sounded horrid on the radio. I would like to offer an explanation about that.
As many of you know broadcast stations employ audio processing to maintain modulation within FCC limits. What many may not be be aware of is that FM auto radios employ a chip that automatically reduces stereo separation and high end frequency response in areas of low signal. The purpose of this is to eliminate static. Unlike AM, FM reception is based on capture. If you are in an area where two nearly equal FM stations are on the same frequency you will hear one and not the other.
With the reduction of separation by blending left and right channels the overall volume can decrease depending on how the particular cut is mixed. Audio is complex in nature: it has both amplitude and phase when one source (channel) is compared to another. While wide separation can be appreciated where the listener is stationed between the two speakers or listening in headphones this is not the case in an automobile.
Some time ago one broadcast equipment manufacturer produced a stereo image enhancer that made many stereo cuts stand out when listening in a home environment. Listening with the two channels combined after that processor resulted in drastically reduced loudness. Another manufacturer produced a similar device which was designed to only operate during certain conditions which did increase the image without sacrificing loudness. A device intended for consumer use was the 801 Omnisonic Imager by Omnisonix, Ltd. This unit had a fixed amount of L-R enhancement and can be a blessing or curse depending on the song.
Audio volume compression was originally employed to make a little speaker sound big. Today we use digital audio processors which are intelligent DSP-based and can produce an excellent sound when properly used. I listen at home using a variety of multiband and single band audio processors and enhancers. I often find listening to the L-R reveals many things, both good and bad.
One short-lived technology that revolved around L-R enhancement was Q-Sound. It failed due to lack of mono compatibility. Audio production is like spice on a meal. It can enhance the flavor or ruin the taste. When properly used it can be very rewarding to listen to.
I have designed several analog processor schemes for AM and FM rock stations. These consisted of modified commercial offerings and some of my own designs. Having a piece of equipment and knowing how to properly use it are two different things.
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crapfromthepast
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| Posted: 12 February 2017 at 3:17pm | IP Logged
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Nice discussion, Tom.
Most conventional stereo recordings are based on amplitude effects. The engineer just makes one channel louder than the other. Both channels remain in phase at all times (i.e., the waveform rises and falls at the same time in both channels).
Interesting things happen when you start introducing delays between the left and right channels. With phase effects, particular sounds can have a delay (intentional or otherwise) between the left and right channels.
Early attempts at mixing in stereo didn't fully grasp the phase issue, so you get abominations like the stereo version of "My Girl", in which the background vocals are completely out of phase between L and R, so that they completely disappear when summed to mono.
Early attempts at intentionally using phase effects weren't so good. The CSG 45s on A&M in the early '70s attempted to simulate stereo using phase effects. And nobody likes the dreaded (E) in the database; to me, "Electronically reprocessed for stereo" translates roughly into "crimes against sound".
Q Sound had a brief flurry of activity in 1990-91. The biggest CD release with Q Sound was probably Madonna's Immaculate Collection.
Some modern-day video games generate some of these phase effects on the fly, and when used with headphones, produce an amazingly realistic soundstage.
But the downside is that these phase effects, without exception, sound awful when summed to mono. FM radio defaults to mono when the signal is too weak/noisy for stereo, so you can imagine that all of these phase-effect techniques were not received well in the radio world.
In my recording studio days in the late '80s, we made extra sure that left and right channels were completely in phase, all the time. We checked our wiring and our cables about once a year, just to make sure. We painstakingly aligned all our tape heads routinely, so that there was no delay between left and right channels. It was kind of a big deal back then.
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There's a lot of crap on the radio, but there's only one Crap From The Past.
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Bill Cahill
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| Posted: 12 February 2017 at 9:07pm | IP Logged
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Yeah Q sound was a disaster at radio. Not only did you have the mono compatability problem (like some versions of quad also had) but some FM stations
bought an audio processor called "phase chaser" and if you played a Q sound track through THAT it was a real mess.
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EdisonLite
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| Posted: 13 February 2017 at 1:36pm | IP Logged
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Very interesting. I'm glad you enlightened us in these posts about this subject. Other than Q Sound (which I strongly disliked on the Madonna CD), I didn't know about any of these other processes/techniques, in terms of what radio was sometimes doing.
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Smokin' TomGary
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| Posted: 13 February 2017 at 4:58pm | IP Logged
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Since there is an interest in my original post I will briefly explain typical audio treatment in AM and FM broadcasting. This will be the edited 45 version of In-A-Gadda-Da-Vida (my apologies to Iron Butterfly).
FCC rules define maximum limits for modulation. In AM it is 100% negative/125% positive. In FM it is +/- 75 KHz deviation which equals 100%. A process known as limiting is used to ensure these limits are not exceeded. Most broadcast stations wish to achieve a limited dynamic range (i.e. keep the modulation as high as possible at all times). This is done using volume compression. Notice I qualified the term using "volume" to distinguish it from digital or lossy compression which is a subject of its own.
Volume compression can be achieved by sampling the output of an audio amplifier and using it to reduce the gain of the stage to produce a uniform output level. That is the analog oversimplified explanation. A problem with this becomes evident with bass heavy or high end heavy songs where that material controls the overall loudness of the material.
One solution is to divide the audio into separate bands using a crossover network. In this way you can compress each band and combine them at the output. Different bands require different timings (attack and release) to sound natural and undistorted.
Popular audio processors are all digitally controlled and perform compression, limiting and FM stereo generator functions. For AM the stereo generator is not used. The design and operation of an audio processor is a careful combination of art and science. The discussion can consume volumes and is well beyond the scope of this post.
Other devices such as microphone processors, stereo enhancers, psychoacoustic processors (such as those manufactured by Aphex and EXR), subharmonic synthesizers such as the dbx BoomBox, and others such are sometimes also used.
Another factor in the vinyl days was sped up turntables. One popular AM station in NYC sped their turntables by +1.5%. At a popular FM station in CT we used Technics SP-10 turntables for on-air use which I modified the logic to produce a +1.333% increased speed. What you heard on the radio would be different than when played at home at normal speed.
This is a tradeoff between loudness and distortion. If clipping is used it can produce excessive distortion if not used properly. A good (or bad) example of this is on "Promiscuous" by Nelly Furtado. Look at the audio output of your CD player with an oscilloscope. Too much or improperly timed compression can cause distortion. Recall I stated audio processing is a combination of art and science. It is a tool. Knowing how to properly use it can yield an excellent sound. Improper use can yield an undesirable sound.
While I could go on I think this brief explanation should suffice. I would be pleased to answer individual questions via email since this topic is on the outskirts of the main focus of this board.
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Top 40 Music on Compact Disc : Chat Board
Topic: How Music Sounds On The Radio
