Singing, and especially emotional expression in opera and lied singing, can be described in terms of a basic unit, called here unit pulse, deduced from Fast Fourier Transform (FFT) spectrograms, and interpreted as a basic brain command to the vocal folds consisting of tightening followed by immediate tension release. This unit pulse, of 100-160 ms duration, is a measure of the degree of excitement in singing. It also defines a unit of time, and serves as a brain time counting mechanism (biological clock) in rhythm. It explains the origin of vibrato and of legato coloratura singing. Each vocal tone is composed of one or more unit pulses. Excitement and calmness can be defined on the microscopic level of a 160 ms time scale, and described in terms of three varieties: large pulse, small pulse, and zero pulse. The various ways of their arrangement within the structure of the tone determine the singer's ways of emotional expression in singing. This is a simplified, more basic code of emotional expression in singing than the high-level emotional expression language presented by the author in a previous work. Biologically, the three varieties of the unit pulse correspond to particular sequences of neural firings in specific patterns. Analysis of performance of vocal music in terms of the unit pulse allows quantitative measurement of the (momentary) degree of excitement for each individual tone along the sung melodic line, and gives an insight into the singers' intentions and personal ways of expression and interpretation.