PART II: Human Hearing, Total Distortion and Loss of Information
Fundamentally, the effect of a poor quality system comprising of inferior electronics, transducers and acoustic design is a lack of definition and detail, but equally important in a live audio situation is the distance in which a system can project clear defined audio.
To maintain high-quality sound, especially at a long distance, it is vitally important that each part of the audio chain is of the utmost integrity. The quality of each component in the signal path will determine the amount of information loss. The system must be capable of transferring an unchanged sound, including the ambience of a performance over distance at the required level to provide the greatest possible experience for the listener. As the area of coverage increases, the demand grows for system resolution and dynamic range. These factors will be determined by the quality and speed of the attached electronics, digital sampling rates, transducers and acoustic design, all of which are key elements of Super Live Audio technology.
Dynamic range is a system’s ability to reproduce the softest signals to the very loudest. In this context, the different signals captured from multiple sources on stage may vary from the threshold of hearing to over 120dB and they should all be replicated accurately by the system relative to the engineers mix of those sources. It is therefore a requirement that when the system is operating at high SPL it has the ability to clearly transmit the low level intricate detail of the performance. For example, we should be able to hear the breath noise of a flute player through the volume of a drum kit.
Dynamic Range is not a pre-requisite of a system’s SPL capability, high SPL does not directly equate to high dynamic range. In fact many systems are delivering high amounts of non-harmonic distortion when operating at high levels. While this may exhibit the system has high SPL capability, this distortion becomes apparent in the high frequency range significantly masking the weaker parts of the signal. This masking has the effect of erasing a large proportion of the detailed information thus causing a significant reduction in clarity. The artificially changed signal makes it impossible to transmit the ambience or real atmosphere of the original sound to the listener, particularly over distance.
Effect of distance on the quality of sound transmission with different quality sound devices
Non-linearity of the acoustic system presents Harmonic Distortion, which is related to the original signal. Multiples of the fundamental Harmonic signal within the spectrum is presented, consisting of even and odd Harmonic distortion components.
Odd harmonic distortion is caused by disturbances in both half-wavelengths of periodic signal, (Typically established at the amplifier limitation). Even harmonic distortion is caused by disturbances in one half-wavelength, (Typically established at high acoustic pressures, as 2nd harmonic distortion is a function of the acoustic pressure). Listening tests show that odd harmonic distortion is audible form 0.1%, whilst even harmonic distortion is audible form 1%.
Non-harmonic distortion is not related to the original signal, it is caused by the slow reaction of the system due to inadequate damping of the acoustic components and filters, and this also creates extraneous noise to be added to the original signal, exhibiting unpredictable behavior of the system. A typical representation and expression of non-harmonic distortion is caused by a long settling time, a low sampling rate and poor DSP processing power.
Non-harmonic distortion is extremely audible depending on the character, but is often confused and mistaken as high frequency content within the original signal, in effect masking the true response and thus is unable to be transferred correctly over distance.
The audio signal consists of many components, harmonics, noises and disturbances across the spectrum and is complex. It is therefore true to say that its properties are closer to random signals. It follows that the distortion of a complex audio signal creates a complex noise level, which masks and disturbs the low levels of the original signal. Just 1% distortion of a complex signal creates a broadband noise floor at a level of -40dB. Practical tests have proven that we can hear a 1Khz sine wave tone with 0dB level with white noise at levels of -70 to -80dB. What this demonstrates is that a high distortion system will completely mask low level signals, i.e. (The color of sound) All-specific designed KV2 Audio transducers and components exhibit extremely low distortion, (below 0.1%, example – you can hear the singer breathing) and this presents new experiences not previously heard of sound reproduction with clear and very high dynamic definition.