Matt Edwards

Associate Professor of Voice, Shenandoah Conservatory Artistic Director of the CCM Vocal Pedagogy Institute

Mix it up Monday: Begin with the source

CCM Bannder no dates

The source-filter theory of vocal production states that it is the combination of vocal fold vibration and vocal tract resonance that creates the final product. When the vocal folds vibrate, they create a series of harmonics.


The Harmonic Overtone Series

The manner in which the folds vibrate determines whether the upper harmonics are strong or weak.


This is an example of the spectral slope. The angle of the slope from left to right gives us information about the closure of the vocal folds. If the slope is gradual, we would say there is more “chest voice” in the sound or that the folds are thick. If the slope is steep, we would say there is more “head voice” in the sound or that the folds are thin. 

As the signal from the vocal folds travels through the vocal tract, the harmonics are then boosted and attenuated (cut) depending on the shape of the vocal tract.


This image shows the resulting formant peaks of the vocal tract position illustrated to the left. The grey zones in the graphs on the right show the vowel formants. The vertical black bars show how the formants boost or cut the amplitude of the harmonics.

In order for us to hear ring and clarity in a voice, the vocal folds must produce enough harmonic information for the vocal tract to do its job. So for instance, if the vocal folds are not producing any energy in the singer’s formant range, no matter how you adjust the vocal tract, you will be unable to create ring in the voice. That is because the formants (resonating frequencies of the vocal tract) have no harmonic frequencies to amplify. The only way to add more ring is to create more harmonic information at the vocal fold level.

This is a much different approach to teaching than what I was taught in my early years of singing. However, the source-filter model is backed by years of scientific research and is deserving of serious consideration and study. When I began implementing the concepts of register based training in my own teaching, the results were stunning.

At the CCM Vocal Pedagogy Institute we focus on this approach during the first session where we explore the viewpoint that technical issues are frequently a result of improper registration and a lack of coordination between the respiratory and phonatory systems. In this approach, the teacher focuses first and foremost on how the vocal folds are vibrating and then creates registration based exercises to improve the outcome. So for instance, if the voice is breathy, the teacher would say that there is too much head voice in the sound (thin vocal fold closure) and would focus on chest voice dominant (thick vocal fold) exercises. After the singer can produce a solid “chest voice” (aka better vocal fold closure), the teacher works on establishing both chest and head dominant mix. This theory was written about extensively by Cornelius Reid in his numerous writings and is also a core concept in the work of many contemporary pedagogues.

As you teach this week listen to each voice and try to decide if the vocal folds are doing what you want them to do. Are they closed too tightly (pressed phonation) or are they not closing efficiently (breathy phonation)? After you identify which end of the spectrum they are singing in, move to the opposite end. So if a soprano has a voice that is weak and airy, go to the bottom of their range (usually around A3) and sustain /a/ vowels at volume 8 to 9 in pure chest voice (read more about the value of sustained pitches here). The sound should be bright, slightly harsh, and may sound like a male voice. Carry that sound up to F#4 and back to A3. Talk to the student about vocal fold closure and help them understand that this work is not about creating a final product, but rather about improving vocal fold closure. When they can successfully sing in a chest dominant production, switch to glides of a 3rd or 5th. Have the student begin the glide in full chest at forte and decrescendo to mezzo forte as they glide up and crescendo to forte as they glide back down. This will help them begin to establish chest mix.

If a belter is screaming their high notes, go to the extreme opposite and have them vocalize on a descending five note scale at pianissimo with a lot of excess air in the tone. This will encourage the vocal folds to relax and not press together so firmly on the upper end. After working on “anchor head voice” for several minutes, have them glide down from five to one beginning with an /u/ and ending with /i/. Instruct them to crescendo on the way down into their mixed voice. This will help them explore new options for the upper part of their voice that do not include pressed phonation. (You can check out additional register blending exercises from Richard Miller here and Dr. Aaron Johnson here).

There are more steps to the process than this, but beginning here serves as a good place for exploration if this concept is new to you. If you really want to dive into this type of approach, consider joining us this summer at the CCM Vocal Pedagogy Institute (for more information click here). We have an exciting line-up of guests who are all committed to fact-based pedagogy and exploring multiple techniques for achieving the same end result.

Do you use the source-filter theory in your teaching? If you do and would like to contribute to the discussion, please leave a comment below. If you are not already following the blog, please sign-up at the bottom right of this page. As always, thank you for reading!



4 comments on “Mix it up Monday: Begin with the source

  1. Dr Daniel K. Robinson
    May 8, 2017

    As always Matthew, you have explained the ‘complex’ in wonderfully simple terms. Bravo! I subscribe (and teach) to the ideals you have outlined above. Where some teachers might think that this approach is too ‘technical’ for students, I have found that many of my students, having already consulted Dr Google, arrive with a baseline understanding and enjoy learning voice through the technical lens.

    As a side, one day I hope to join you for the CCM Vocal Pedagogy Institute Summer School…but for now, I’ll have to content myself with reading your excellent posts.


  2. Dorothy Thorpe
    May 13, 2017

    Thank you, Matthew. I have tested your suggestion for breathy voices on a couple of students this last week and have had instant results especially with an eleven year old girl. FYI I recently completed the all 3 levels of Somatic Voiceworks the Lovetri method in Australia Jan 2017.


  3. Pingback: Mix it up Monday: How to allow placement to reveal itself (pt. 1) | Matt Edwards

  4. Pingback: Mix it up Monday: How to allow placement to reveal itself (pt. 2) | Matt Edwards

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This entry was posted on May 8, 2017 by in Misc. Thoughts, Mix it up Monday, Registration.

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