Hearing System Model and Sound Quality Estimation

The feasibility of and the necessity for an objective estimate of the psycho physiological perception of sound after compression are discussed. Some possible methods are studied. The preferable method is the consonance method. The essential principles of this method are offered algorithm of human auditory system and musical theory. The method and measurements results are discussed. Key-Words:redundancy, consonance, dissonance, sound distortion Introduction It is well known, that in sound signal transmission including the transmission of music signals, the information has redundancy. This redundancy is divided into two parts: statistical redundancy, which is caused by correlative relationships between individual signal values, and redundancy related to properties of the auditory perception. It may be more efficient to divide all information into four parts, as shown in Fig.1, where: 1. Statistical redundancy. It is possible to cut away this part without a loss of information. However, in this case the transmission method may be more complicated and left over signal is more fallible. 2. Psychological redundancy. This part can be neglected as well provided that we have the complete knowledge of human auditory system. Besides, in the case of durable sound recording, one should take into account that in future all information may be necessary. 3. ”Information coloring”. This part of information is not related to the content of the announcement. It is the way the announcement is made (i.e. the ”coloring” of the information). For example, the following sentence ”Nigeria won against Switzerland 3-0 in the world-cup” sounds different in these countries. The partial decrease of this part may not be perceptible if a listener does not know who is speaking or playing. Moreover, this part of the information may not be interesting for the listener; furthermore in some cases this information is undesirable (for example, special operations). 4. ”Meaning part” of information. This is the content (i.e. the content of the announcement, the melody and the tonality of the music). This part of information should not be decreased. Even if raising the communication efficiency is desirable (which is closely related to 1, 2 and 3), the ”meaning part” should not be changed at all times. Therefore the change of this information can be the basis of an objective method for quality estimation of compression systems.