# Real-Time Visual Feedback in Singing Pedagogy: Current Trends and Future Directions
## 2 The Respiratory Subsystem  
### Breathing Patterns  
Breathing behaviors are crucial to determine voice quality and, therefore, play an important role in voice pedagogy. Terms such as 'appoggio' and'support' are extensively used, referring to the coordination between laryngeal and breathing events [21; 22]. Also, less efficient phonatory habits, such as the habitual use of pressed phonation (hyperfunctional), can been modified as a consequence of altering breathing patterns [23; 24]. However, finding an optimal breathing strategy for a particular song is highly idiosyncratic. On the one hand, different muscular strategies can be applied depending on the singer's individual characteristics [18]. For example, some singers mainly use the ribcage to vary lung volume, whereas others also recruit the abdominal wall to either assist with changes in the ribcage or stabilize it [25]. After inhalation and just before a phrase starts, singers have been found: (1) to apply a slight contraction of the abdominal wall [26]; or (2) to modify ribcage volume [27].  
Visual feedback of trans diaphragmatic pressure can help both trained and untrained singers to direct their attention to the act of contracting the diaphragm [23]; such feedback might contribute to developing an optimal breathing strategy. Breathing patterns during singing have been monitored using magnetometers [28], optoelectronic plethysmograph [29] and respiratory inductance plethysmograph (RIP systems) [25; 30]. RIP systems are relatively easy to manage and allow for the generation of real-time feedback [31]. An example is the RespTrack system (by [PERSON], available at www.columbi.se, accessed on 6 June 2022). It has two elastic belts that should be placed-- one around the ribcage and the other around the abdominal wall (Figure 2). These belts are connected to a unit equipped with an on-board AD-converter and a reset button. A potentiometer knob allows for varying of the balance between the ribcage and abdominal signals so that they reflect lung volume. The unit has outputs for volumes of the ribcage (RC) and the abdomen (AB) and their sum, which, when accurately balanced, corresponds to lung volume (LV).  
Figure 2: (**Left**) RespTrack unit; (**Right**) placement of belts monitoring ribcage and abdominal wall movements.  
The RespTrack unit can be connected to a portable computer with a USB cable. The RespTrack Recorder software (Columbi Computers AB, Stockholm, Sweden) visually displays RC, AW and LV signals simultaneously in real-time. To record these signals, data acquisition devices or audio interfaces with direct current-coupled inputs are required; the signals are slowly varying and, therefore, cannot be recorded with normal sound cards.  
Figure 3 displays audio, LV, RC and AW signals, recorded with a microphone and a RespTrack unit for a female jazz singer performing a phrase from an aria with, at the top, the audio signal of the phrase, and below, the LV, RC and AW signals. The red box highlights the inhalatory behavior, showing the expansion of AW and RC and the associated increase in LV. Note that the AW is contracting during the first part of the phrase. This breathing behavior is consistent with previous descriptions [26].