century have stressed their pleasant/unpleasant, or agreeable/disagreeable character. This may be justifiable in a psychophysiological context, but much less in a musical context properly speaking: dissonances often play a decisive role in making music pleasant, even in a generally consonant context—which is one of the reasons why the musical definition of consonance/dissonance cannot match the psychophysiologic definition. In addition, the oppositions pleasant/unpleasant or agreeable/disagreeable evidence a confusion between the concepts of "dissonance" and of "noise". (See also Noise in music and Noise music.) While consonance and dissonance exist only between sounds and therefore necessarily describe intervals (or chords), such as the perfect intervals, which are often viewed as consonant (e.g., the unison and octave), Occidental music theory often considers that, in a dissonant chord, one of the tones alone is in itself deemed to be the dissonance: it is this tone in particular that needs "resolution" through a specific voice leading procedure. For example, in the key of C Major, if F is produced as part of the dominant seventh chord (G7, which consists of the pitches G, B, D and F), it is deemed to be "dissonant" and it normally resolves to E during a cadence, with the G7 chord changing to a C Major chord. Acoustics and psychoacoustics Scientific definitions have been variously based on experience, frequency, and both physical and psychological considerations. These include: Numerical ratios: in Antiquity, these mainly concerned string-length ratios. From the early 17th century onwards, frequency ratios were more often considered. Consonance often is associated with the simplicity of the ratio, i.e. with ratios of lower simple numbers. Many of these definitions do not require exact integer tunings, only approximation. Fusion: perception of unity or tonal fusion between two notes and/or their partials. Coincidence of partials: with consonance being a greater coincidence of partials. By this definition, consonance is dependent not only on the width of the interval between two notes (i.e., the musical tuning), but also on the combined spectral distribution and thus sound quality (i.e., the timbre) of the notes (see Critical band). Thus, a note and the note one octave higher are highly consonant because the partials of the higher note are also partials of the lower note. Dynamic Tonality: Like "Coincidence of partials" above, Dynamic Tonality considers consonance to arise from the alignment of partials with notes (as per the video at right; see also Dynamic timbres). Dynamic Tonality