Sound compression. What is it? To answer that, we have to know what is dynamic range first. Simply put, dynamic range is the difference the loudest and softest sound that a human can hear. Or, the difference between the loudest and softest sound in a recording.
Dynamic range is measured in decibel (dB). Decibel is a logarithmic measurement meaning it's a ratio (comparison between two numbers) and not an absolute. In acoustic (or sound), decibel is a logarithmic measurement of power. Sound is always a measurement of two levels (loudest and softest). The math formula 10 log P2/P1; where P1 and P2 are two different levels of the same sound and logarithm is to base 10. If there's a difference of 10 times between the two levels, so that 10 log (10/1) = 10dB. A double of power (or loudness level) produces 10 log (2/1) = 3.01029 (rounded up to 3dB).If you halve the power (or loudness), you reduce it by 3dB. If you double the loudness, it's a 3 dB increase in power. Simply put, loudness or power is doubled for every 3dB increase. That's all you have to remember.
Now, on to compression and the tools needed for it-a compressor. What is sound or audio compression and a compressor then?
"A compressor is a signal processing tool or equipment to reduce an input (sound) signal to a predetermined level when the signal exceeds a certain level (called a threshold level). And by reducing (attenuating) the louder signals, the compressor reduces the signal's overall dynamic range. The range between the loudest and softest signal (ie. dynamic range) is now "compressed".
That's not the end of the story however. The compressed signal which now sounds softer has to be 'compensated' by increasing its level again. Consequently, by increasing the signal's gain, the average level will be greater. Thus the signal will be perceived to be louder." There are other variables in play like attack time, release time, compression speed but they're too technical to explain, even for me.
In short, compressors are like automatic volume control to reduce sound level or volume when it's too high.
There are a few areas where compression is needed.
1) To minimize the changes in volume when certain segment of music has too great a dynamic range. This could cause the softest signal to be barely audible to listeners (no i didn't hear that soft, sexy whisper la). Or the loudest signals to be too painful to listen to.
2) To balance out the sound of different musical instruments so that one instrument do not 'drown out' the sound of another eg. a loud horn may easily drown out the vocals of a soft, sexy female singer. And of course, we have...
3) To enable a signal to be made significantly louder in the mix while increasing the overall signal-level reading on the meter only slightly. This is done by increasing the ratio of average-to-peak levels (refer to graph at the end). In layman's term, average levels are the sound level a piece of music that we hear most of the time (say perhaps, 98% of the time lah); and the peak level is only heard for around 2% of the time (ie. when a drummer suddenly hits the snare or cymbals).
Our ears are sensitive to average levels (root mean square, rms in audio jargon) of sound and loudness, not its peak. For those old enough to remember, those days manufacturers of consumers hi-fi and stereos equipments always state their output power in their own industry jargon PMPO (for peak music power output, i think); something like 1000 watts of PMPO for an equipment of maybe 10 watt rms output. But we all know it's a marketing strategy to push sales.
Compression of music should be done moderately, only to enhance the sound of a recording not to make it louder. i'm saying this as a music lover and consumer.
-taken from the book 'Modern Recording Techniques' (change some words).
In today's scenario, the producers of music tends to record music "hot". Very, very hot in fact. These levels are way above the normal operating levels without distorting the music. But if we listen to today's music, distortion is already running rampant. Their logic for doing this? Economics again, of course.
Maybe they hired psychologist to study human behaviours first before doing this. To study what the masses would want to listen to and manipulate the way it should be listened to. And then influence them again on what they should listen to. Who knows?
Listening to a few modern cd recordings like u2's "How To Dismantle An Atomic Bomb", The Goo Goo Dolls "Greatest hits Vol.1, will cause ear-fatigues after only a short time. Modern rock recordings are mostly unlistenable. There is no musical highs and lows anymore. Just constant wall of sound. Very high wall that is. How to appreciate any subtleties in music, if there are any that is. Details and nuances are what convey emotions, not crass loudness. Same can be said of politicians then, no?
Well, music is a multi-million industry and very competitive business. And broadcast radio is still an important medium to sell those singles and cd's. You want your artistes and their music to stnad out from the rest, well the music as loud as possible. Drown out the competitors. Today's listeners want more kick in their music. More bass; the lower the much better. More sweet highs from those guitar licks and cymbal crashes. A 1 or 2dB increase would achieve that effect. Let's put in another 6dB then. Yes, more and more of everything is the cry of the new generation. Now, why would we not want to satisfy their desire?
Why do music sound so much more better in the past? In the 60's, 70's and my favourite, the 80's. One word, the emotion conveyed. Let's not talk about the memories they evoke. Today's music will evoke different memories for today's generation in 10 or 20 years time.
Young people will say there's so much great music today. Maybe so. But today's great music is very different from the past good music. We have enjoyed uninterrupted prosperity for the longest time. It gets reflected in the music. Young people don't want to listen to good music. Most just want to have a good time and any catchy pop music will do. Or perhaps good music doesn't get out from their creators to the everyday average listeners.
Musicians don't want to make great music. They want to make sell-able music. They want fame and fortune. To be adored by fans. Telling a story and investing the story with emotions to an audience? Only if we can become famous and make lots of money. Why not.
With the digital age, there comes 'free' music, or general public perception that music should be free. Now why should it be free? Even in economic terms, which everyone today is fond to speak of, music is also a product. Like cars or wine, a piece of music is a product of a person creativity. We want to consume a product, we pay for it. Supply and demand. There's no free lunch unless it's welfare. No good musician would want welfare. Even buskers on the street have their own incentive to play. They would want listeners and admirers to compensate them, even if it's a small token or some clapping maybe. Incentives do not have to be in a financial form. Economics do play a part in everyday lives.
Do people still listen to music in a traditional way? What's that? Using stereo equipments lah. Not ipods, computer speakers, or mobile phones. Or has it become old-fashion and passe already? What's with ringtone 'music' these days. Some says it's even music. Or perhaps the world has changed and moved on while i still stays the same...
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Chart Showing The "Evolution" of Recorded (CD) Music Levels
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Resulting From "The Level Wars"
- 18dB
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- 12dB
|
- 6dB
|
- 3dB
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0
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1985
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1990
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1995
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2000
|
2002
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2005
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2007
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| = Average Signal level - Not Peak Level |
| = Available Headroom For Punch / Musical Peak |
The blue bars in the graph represent the average level (not the peak level) of signals, and gives us our sense of perceived loudness. The gray bars, the difference between the average signal level and digital zero, are areas reserved for musical peaks.
It's the gray bars that provide the punch in music. As the average level is raised using compression (more blue, less gray) the signal gets louder, but dynamic range is reduced. This produces a flat, boring sound, without punch, impact, or emotion. It also results in reduced clarity. Digital clipping can be heard in many commercial CDs produced since 2002.
For an animated display of the loud CD trend, click Here.
The above is a study calculating the average level of popular CDs from each of the time periods indicated. The average level of a sine wave is 3dB below its peak level. When listening to recorded music with a peak to average ratio of less than 3dB (2002 - 2007) you're listening to harmonic distortion (with a beat).
Source: cdmasteringservices.com
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