Dr Bunsen Honeydew
16-08-2011, 14:09
It seems there is a widespread misunderstanding about this psycho acoustic effect, so I feel perhaps an explanation is in order.
Firstly psycho acoustics relates to things that cannot be measured as such as they are part of our genetic programming as human beings. This is our nature and on top of this is imposed our nurture, which are the things we think we know, or we have been told and have taken on board as part of our perceived reality or our nature.
The "nature" of loudness is a self protection mechanism. When a sound is too loud for our physical nature to reproduce naturally we have a protection mechanism, wincing, placing hands over ears etc. What are we reacting to? we are reacting to mechanical distortion created by the physical structures of our ears reaching overload or mechanical clip, and our mind is programmed to realise when we are approaching this so we back off, move away from the danger if we can. This overloading of the ears mechanical structure means that harmonic distortion is created, so the ear hears the onset of harmonic distortion as the onset of something dangerous.
Now a sound system also creates these harmonic distortions when it is overloaded either mechanically or electrically, so even if those level have not reached a point where they threaten your hearing the brain will interpret them as *loud* and potentially dangerous so you react. It also will react to the onset of this distortion before the distortion is actually apparent as musically destructive, and the minds defence is to tell you it is loud. Now nurture comes in if you have been brought up on live rock concerts or similar to actually want to have that effect.
Now my point in all this is that this will happen with a two watt radio, a 50w hi-fi system or a 1000w pa, and with all three it will happen at onset of distortion. Though with the radio we intellectualise that it is not going to hurt us, where as the 1000w PA system is seriously capable of hurting you and if you are close enough then even killing you, without you necessarily perceiving it as loud musically, all the distortion will be from the destruction of your ears as they start to bleed.
It can be simply broken down to reaction, and being words obviously different people interpret differently, but if we take a norm then if you are listening to a high powered system, or efficient, or in a small enclosed environment your reaction is normally "wow that is powerful". If you are listening to a system going into transient clip your reaction is more likely to be "that is getting loud". The latter is the psycho acoustic loudness effect.
Now we come to how that is affected by hi-fi design. There is an internationally accepted standard for matching hi-fi items together known as line level (there is also mic level, which applies to other mechanical source transducers like cartridges). If a product is active then it is designed to operate at line level, and I know of no professional and commercial company that deviates from this apart from in the case of passive pre-amps. So a product operating at line level using a LogA or LogB or even Linear law volume control when it reaches 75% of travel will be clipping *all* signal of a transient nature. With modern highly compressed recordings this will be even more of a problem as transient almost becomes normal signal level.
Now we get to the point of the other thread that was closed. A valve amp will be musically far less noticeable in this than a solid state amp, due to the nature of the harmonics they produce when overload starts. BUT both will induce the psycho acoustic loudness effect.
Firstly psycho acoustics relates to things that cannot be measured as such as they are part of our genetic programming as human beings. This is our nature and on top of this is imposed our nurture, which are the things we think we know, or we have been told and have taken on board as part of our perceived reality or our nature.
The "nature" of loudness is a self protection mechanism. When a sound is too loud for our physical nature to reproduce naturally we have a protection mechanism, wincing, placing hands over ears etc. What are we reacting to? we are reacting to mechanical distortion created by the physical structures of our ears reaching overload or mechanical clip, and our mind is programmed to realise when we are approaching this so we back off, move away from the danger if we can. This overloading of the ears mechanical structure means that harmonic distortion is created, so the ear hears the onset of harmonic distortion as the onset of something dangerous.
Now a sound system also creates these harmonic distortions when it is overloaded either mechanically or electrically, so even if those level have not reached a point where they threaten your hearing the brain will interpret them as *loud* and potentially dangerous so you react. It also will react to the onset of this distortion before the distortion is actually apparent as musically destructive, and the minds defence is to tell you it is loud. Now nurture comes in if you have been brought up on live rock concerts or similar to actually want to have that effect.
Now my point in all this is that this will happen with a two watt radio, a 50w hi-fi system or a 1000w pa, and with all three it will happen at onset of distortion. Though with the radio we intellectualise that it is not going to hurt us, where as the 1000w PA system is seriously capable of hurting you and if you are close enough then even killing you, without you necessarily perceiving it as loud musically, all the distortion will be from the destruction of your ears as they start to bleed.
It can be simply broken down to reaction, and being words obviously different people interpret differently, but if we take a norm then if you are listening to a high powered system, or efficient, or in a small enclosed environment your reaction is normally "wow that is powerful". If you are listening to a system going into transient clip your reaction is more likely to be "that is getting loud". The latter is the psycho acoustic loudness effect.
Now we come to how that is affected by hi-fi design. There is an internationally accepted standard for matching hi-fi items together known as line level (there is also mic level, which applies to other mechanical source transducers like cartridges). If a product is active then it is designed to operate at line level, and I know of no professional and commercial company that deviates from this apart from in the case of passive pre-amps. So a product operating at line level using a LogA or LogB or even Linear law volume control when it reaches 75% of travel will be clipping *all* signal of a transient nature. With modern highly compressed recordings this will be even more of a problem as transient almost becomes normal signal level.
Now we get to the point of the other thread that was closed. A valve amp will be musically far less noticeable in this than a solid state amp, due to the nature of the harmonics they produce when overload starts. BUT both will induce the psycho acoustic loudness effect.