In June 2007, 2012 and 2014 Julian McGlashan and Cathrine Sadolin performed endoscopy studies and endoscopy/high speed studies in 2012 and 2014 at CVI in Copenhagen.

Twenty-one singers (ten males and eleven females) in 2007, thirteen singers (seven male and six females) in 2012, and sixteen singers (seven males and nine females) in 2014, a total of 32 singers (fifteen male and seventeen females), trained in the Complete Vocal Technique were recruited and asked to produce a sustained vowel in each of the four modes and then adding growl to that that mode. Subsequently they were asked to alternate between the ‘clear’ mode and the mode with growl.

17 subjects had pictures that we could analyse for this particular study, so the rest were excluded as they could either not tolerate the examination, did not perform the growl correctly, or the image quality was not adequate for interpretation.

Each singer was examined using an OTVS7 camera (Olympus) and ENFV2 videoscope (Keymed) coupled to the Laryngostrobe (Laryngograph) digital capture system. Laryngograph electrodes were positioned over the thyroid cartilages and an omnidirectional microphone placed at distance from the singer which allowed recordings at all levels of loudness. Also the ELG and acoustic signals were captured and analysed with the Speech Studio (Laryngograph) software program.

Each set of modes (with and without growl) video images were analysed by Julian McGlashan and Cathrine Sadolin and the appearance and relationship between the key anatomical features was agreed by consensus and documented.  The consistent features were identified and descriptive and explanatory text to aid pattern recognition.

The Laryngeal gestures are more to be seen as patterns of progression from mode to mode, rather than aboslutes. The progession in the patterns can be used as guidelines on how to identify the modes within each singer.

For the growl these are the parameters we looked at: the anterior posterior narrowing, the shape of the pirriforma fossa, the hight of the larynx, the pharyngeal wall, the epiglottis and the arytenoid/cuneiform complex when it was possible.

Not only did we look at what was changing between using the mode and the mode with growl, we also looked at what was actually vibrating.



To get a better understanding of the laryngeal changes associated with growl and to examine the interaction of supraglottic vibration during intentional growl.



We gave the various parts in the vocal tract levels in order to identify and specify on which levels the various changes take place. The levels also make it easier to communicate where the changes take place. On the video from the footage only the level 3 and 4 are seen. For more info on the level, click here.


Still of Growl 

still growl



Still of vibrating cuneifrom 

still  cuneiform



When we look at the video examples of the mode with and without growl. The Growl was produced by anterior-posterior narrowing of the supraglottic structures and quasiperiodic vibration of the aryepiglottic folds. This was seen well in 3 subjects and inferred in 5 others as only brief glimpses of the tips of the aryepiglottic folds or cuneiform cartilages were seen as the epiglottis was angled posteriorly. In 7 subjects we saw glimpses of tips cuneiform cartilages appearing to vibrate against epiglottis.



Growl can be done safely.

Notice that the waveform of the vocal mode is maintained during the growling.  This indicates that the vibrations of the vocal folds are unhindered and unaffected by the growl. So the vocal folds are vibrating freely under the growl. This makes sense because the we know that the growl is taking place higher in the vocal tract and not on the 1st level (the level of the vocal folds).


In all the examples where we can see the vocal folds, or look at the laryngograph trace, there seems to be a resonably regular pattern, and there didn’t appear to be any evidence of the effect (or any additional noises) being produced in the vocal fold level.

There was evidence on endoscopy or from the Laryngograph of periodic vocal fold vibration.

It need a good technique to ensure accurate vocal mode setting done correctly and an intentional application of the effect.


This information comes from a study effects with the title ‘Can vocal effects such as distortion, growling, rattle and grunting and be produced without traumatising the vocal folds?’. This study was presented by Julian McGlashan at PEVOC7 conference in Groningen, Netherlands, 2007.

This study with the title ‘Analysis of the mechanism of effects such as Distortion, Growl, Grunt and Rattle used in a healthy way by 18 professional singers’. was presented by Cathrine Sadolin at Pevoc 10 (Pan-European Voice Conference) Prague, Czeck Republic, August, 2013.