# Real-Time Visual Feedback in Singing Pedagogy: Current Trends and Future Directions
## 4 The Resonatory System
### Spectrographic Displays  
There are two types of spectrographic displays: spectrogram and spectrum. The underlying analysis can be performed with a narrow- or wide-band filter. The former provides information on individual spectral components and the latter on spectral envelope peaks and valleys.  
Figure 15 provides examples of narrow-band analyses of the word yes, spoken with an ascending pitch. The left panel shows the spectrogram, where the vertical axis represents frequency and the horizontal axis shows time, with grey scale representing amplitude [4,9]. This figure visualizes the changing spectrum peaks, i.e., the formant pattern. The right panel shows the spectrum for a single moment in time (few milliseconds) of the vowel/\(\varepsilon\)/. Here, frequency is run along the horizontal axis and intensity along the vertical. The individual harmonic partials are displayed as vertical spikes.  
Figure 16 visualizes a wide-band analysis of the same utterance. In the spectrogram (left panel), individual partials cannot be seen, but rather the formant peaks in the spectrum envelope. The first formant starts at a low frequency for the vowel /i/ in yes and rises to a high frequency in the vowel /\(\varepsilon\)/. At the same time, the second formant starts at a high frequency and changes to a low frequency. The spectrum (right panel) shows no individual harmonic partials, but rather spectrum envelop peaks at a given moment of the /\(\varepsilon\)/ vowel.  
Figure 15: Spectrographic display of the word “yes”, pronounced in an ascending pitch, displayed by the software Praat (by [PERSON] and [PERSON]) as a narrow-band spectrogram (**left**) and a narrow-band spectrum (**right**).  
Both spectrograms and spectra have been applied in the voice studio for visualizing, for example, voice onset, i.e., the manner in which the voice is initiated [4]. An onset can be breathy if the increase of \(p_{\text{sub}}\) is prior to glottal adduction and vocal fold vibration. If hard, adduction occurs first, followed by a rise in \(p_{\text{sub}}\) and, hence, vocal fold vibration. The staccato onset is typically produced with a simultaneous start of glottal adduction and \(p_{\text{sub}}\) rise and, hence, also of vocal fold vibration [8]. In addition, expressive elements of singing, such as legato, vibrato, ornamentations and intonation, can also be displayed by real-time spectrographs [17; 65; 66; 67]. Moreover, the synchronization of singing and piano accompaniment can be visualized and, thus, improved [4]. Finally, several singing teachers use spectrographs to fine-tune vocal tract resonances in accordance with the aesthetic demands of the music style [9; 16; 57; 58; 60; 61; 62].  
Spectrograms are also quite useful for visualizing register breaks, phonation types, intentional voice distortions and intonation. The visualization of such events can be relevant to voice pedagogy for three main reasons. First, it can assist with the training of intentional voice breaks for expressive purposes, i.e., in yodeling. Second, as register breaks normally occur at specific pitches, depending on voice classification, visualizing spectrograms may help the teacher to classify a voice [68]. Third, it can aid the learning of vowel modification for equalizing voice timbre across the whole vocal range [69].