COLIN WONFOR: Time coherence

Mr. Wonfor / Mr. Elsdon. Am I correct in thinking that correct time coherence of all frequencies is inherent in music? If I have understood this them I guess it means that the sound of a human voice, for example, is time-coherent in all frequencies in a waveform that in itself is a specific time unit.

My belief is that most hi-fi systems rip apart the timing of a tone into a slower bass frequency and faster high frequencies. So the sound pattern is unnatural and can't be identified correctly. Am I barking up the wrong tree here? Raf Osborne.


Hi Raf, a odd question, firstly ripping apart the signal and changing the frequency should not happen in any audio equipment. As to the sound pattern I hope you mean what you can see on a oscilloscope, this will show you what happen when you mix audio together and the harmonics of the mix, and this is natural.


Well, if we take a simple example where a person is playing a piano in a concert hall, is the sound that a member of the audience hears time-coherent? No, just think of all those reflections, absorption by materials and people. Put the piano in an anechoic chamber and is the sound time-coherent? Better but still no. Why? Reflections from the piano, the pianist and possibly the listener.

In the same way playing a recording of the piano on our hifi leads to exactly the same problems. This is why there are electronic devices to monitor sound in a room and adjust the responses of the hifi system to compensate for room resonances.

I cannot speak from experience but I would suggest that any changes that the electronics may make would be swamped by the room behaviour.