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Date:
june 2009
Author:
Peecker Sound
Research dept
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| News |
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| "NO BASS, NO FUN". The Peecker Sound intelligent dynamic processor |
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If we observe the behaviour of young people in a discotheque at the various sound levels, it's easy to see that excessively low sound pressure levels do not excite them in the least and tend to push them away from the dance floor. Only music at a high level seems to attract, hold, and engage them fully. So we could establish a sort of acoustic rule according to which the management of an entertainment venue should never play music at low level, with the risk of making all the patrons flee. The reality is a bit more complex and requires a more in-depth psychoacoustic analysis. The sense of rhythm lies in the perception of the low notes: to be fully engaged in the music, our bones have to be "massaged" by myriad low notes: deep, enveloping, full, and dense.
So we could say "no bass, no fun".
At this point, we will take an in-depth look at how the human ear perceives the various notes (low, middle, high) of the musical scale. The auditory system is highly sensitive to the middle frequencies (voice, guitar, flute, etc.), but can only perceive the low notes with much greater difficulty. In other words, we perceive the low frequencies only when they are at high level, as explained clearly by the Fletcher-Munson curves, measured for the first time in 1933 at the AT&T Bell laboratories.
We can perform a simple experiment on the piano. With a forceful and decisive action, press a central key and then another one all the way down on the left of the keyboard: the instrument plays two equally intense and powerful notes. Then, gently brush your finger over the same two keys: while the central note will still be perfectly distinguishable and clear, the lower note will now appear to be weak and muddled, just barely perceivable and uninteresting. We can therefore see that our ear is an amazing mechanical apparatus that is highly sensitive to the frequencies around 2-3 kHz, but picks up the low notes only when they are very intense. Another simple example: while we are intently reading a book, the hum of a mosquito is all it takes to disturb us, but we don't notice the rumble of faraway thunder.
Now let's go back to our dance floor. Let's suppose that music is being played at a level of 100 dB and the low, middle and high notes seem to us to be well amalgamated, balanced, and pleasantly engaging. We lower the level to 90 dB: the low notes disappear immediately, the balance dissolves instantly, and the faces of the audience, while satisfied before, will now show signs of annoyance.
What happened? In the diagram of sound levels with the nice linear curves of Fig. 1, we have gone from the curve 100 to the curve 90, while the ear's perception has dropped significantly at the low and high frequencies (Fig. 1 again). The catastrophic effect of sound sensation is not due to the diminished sound pressure, but to the heavy drop in sensitivity to the low notes.
Naturally, all this is exacerbated by the conditions of modern society: the noise of traffic, in the office or workplace, mobile phones ringing, neighbours making a racket and so on, have considerably reduced the sensitivity of the human ear. Scientists have found that the Australian Aboriginal people, at seventy years old, have curves of acoustic sensitivity similar to those of our thirty-year-olds.
Averting this anomaly requires a system that can generate different response curves at the various levels (see Fig. 2).
The Peecker Sound R&D Department has developed an intelligent dynamic equalizer that is able to compensate for the variations in sensitivity of the human ear related to the varying sound levels. This device incorporates "intelligent" circuits that continuously compare the frequency response with the average sensitivity curves, adjusting them until an equal perception over the entire spectrum is achieved.
If, for a certain sound pressure level and at a certain frequency, say 50 Hz, our ear loses, for example, 7 dB of sensitivity, this super-intelligent dynamic equalizer raises the response to the same frequency by the same 7 dB. So what is the practical effect? The listening remains identical, with the same sensation and same quality, at any sound pressure level.
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