Brains and Membranes

Bassoon Reed Making by Christopher Millard

Chapter 16 – Corvids and Cacks

As if holding a bassoon weren’’t funny enough, we seem to get an inordinate number of laughs just testing our reeds.

We all ‘crow’ on our reeds – but to what end? What are we looking for? Rattles, peeps, honks, caws, croaks, cackles, rasps…squawks??

Time for a quick review. Remember that in a coupled system [bassoon + reed] there are strong bore resonances which determine the periodic oscillations of the input device. But how long does that bore need to be to exercise control? The shortest bore we use is open F; it’s the last rung of that fundamental first ladder from Chapter 13. Upper register notes are based on longer bore lengths, utilizing higher harmonic resonances, which are corrected for tuning by employing complex fingerings.

We can make an even shorter coupled system – just the bocal and the reed. Most of us play on setups where this combination delivers between C3 and C#4. The internal volume of the bocal has its own standing wave behaviour that dominate the reed’s frequencies and creates its own fundamental and harmonics.

Here is a spectrum graph showing what’s contained within that short bocal/reed system. You’ll see similar graphs for any of the notes on that first harmonic ladder.

 

Everything makes sense. It’s sounding 270hz [between a C and C#] which is quite typical for this combination.  The harmonics are all true to the harmonic series.

If we were to start cutting the bocal shorter and shorter at its large end – admittedly a rather expensive experiment – we’d find the sounding pitch getting higher and higher.  Eventually, we’d toss that last bit of metal tube and have the reed all on its own.  By shedding all the expensive parts, we’re left with the world’s smallest bassoon.  And as long as you blow gently, you will get a fundamental and harmonics by peeping on the darn thing.  This next graph shows an analysis of the harmonic components of the simple peeping sound from the reed by itself.

Amazing eh? A functioning coupled system created with a little bit of cane, wire and string. The first harmonic at H1 is 370 hz [F#4] and the next 3 strong harmonics are at 740 hz, 1120 hz and 1480 hz. Simple integer multiples indicate a pure harmonic series.

Now, as we all know too well, as soon as you start blowing a bit harder something strange emerges. We call it a crow. It’s actually a completely separate acoustical phenomenon – a multiphonic. Yes, just like the fancy multiphonic fingerings utilized in some contemporary music but without all those difficult cross fingerings.

So, what’s going on with this cackle? Let’s take a look. Here is the same reed [shown above in its peeping state] but this time ‘overblown’ into a multiphonic crow:

As you can see, there is still some residual evidence of the original peeping fundamental at H1 and H2, though lowered in pitch a bit. But look at all the other components. H3=1020 hz and H4=1360 hz point to further disorder above. These upper frequencies don’t fit into the integer calculated harmonic series, and they are highly unpredictable. Repeated tests of the spectrum of a crow gives a huge range of variability in these higher inharmonics. This volatility is entirely expected due to the extremely weak bore resonance for the internal volume of the reed alone. The resonances for this tiny volume are too weak to adequately dampen and control the very broad range of frequencies ‘contained’ within the reed membranes. So, the peeping pitch is easily overblown, creating wild non-harmonic components. The ‘crow’ is born.

My kingdom for a rooster.

Continued blowing, especially with newer reeds, often reveals yet a third state with the emergence of an ugly CACK, breaking up the multiphonic itself. You can overblow what is already overblown!!

The next graph shows the same reed, but now operating in this rather pathetic third state.

A different primary frequency has jumped out, H1=540 hz, a quarter tone sharp C5. This bears no relation to the reed’s original peeping pitch whatsoever; it’s just a strong natural frequency for the membranes themselves. Additionally, the other components from H2 thru to H6 don’t fit a harmonic series. Not until the very strong H7=1080 hz do we get a 2nd true harmonic [and another at 3240 hz] of the CACK frequency. And because all of these components remain undampened by strong standing waves they are more subject to frequency alterations caused by blowing pressure. When the reed is unattached to the strong bore resonances of a bassoon IT’S THE WILD WEST!!

So, we start with something predictable [the peeping pitch] and move to the crow [mostly multiphonic] and then often a third kind of wild behaviour. What does it all mean?

You will recall that early on in this blog I referred to a general misunderstanding of the crow. I referred to the assumption that the bassoon magically transforms cackling crows into all the notes on the bassoon. I’m hoping that the earlier chapters explaining the bassoon/reed dialogue has persuaded you to think of sound production as a two-way process.

Is there an ideal crow?

Different players look for different multiphonic mixes, and even within an individual’s reed box there will be considerable variety. Crows can reveal to the bassoonist how likely each reed may respond to certain aspects of the bassoon’s acoustical needs. We learn empirically how to associate certain crows with certain outcomes. Big, complex crows are typically indicators that a reed will be strong in the bottom end and have a large dynamic range. Small, simpler crows are usually associated with softer sonority, reduced dynamic range and limited character.

Different sizes of reeds require different peeping and crow behaviours. Larger dimension reeds typically have less overall compliance and will peep at a higher fundamental frequency. Smaller reeds tend to have greater overall compliance and need to peep at a lower fundamental. The character of a crow is associated with membrane profiles, which are themselves optimized to reflect the physical dimensions of the reed.

Remember that in the MCA model size is modified by compliance. Peeping pitches also reflect that relationship. Your narrow reed may peep at a D, my wider reed at an F# – yet both fulfill the formula for the missing conical apex. Equally important, each player’s comfort zone in terms of combined embouchure and air effort will lead them to choose higher or lower peeping pitches.

The variability of reed dimensions and of performers’ physiological preferences suggest that there is no correct crow. There is an unpredictable relationship between crow and bassoon tone that can frustrate expectations. We are often surprised by what we get when we begin to play. Sometimes a crow just reveals how well that reed crows… Have you noticed that a reed crow will vary according to who is playing it?

Over the years I’ve had students call to crow on a reed over the phone [more recently by video chat…]. But it’s very difficult to analyze while someone else is doing the crowing. We need to be the one doing it – sensing the resistance, placing the lips, opening up our oral cavities. Testing a crow is all about the real-time process of producing those multiphonics – what your breath and your embouchure do to create your crow.

So here is my simple advice. Analyze your crows not only by what you hear, but also by what you do to make the crow happen.

Next week in Chapter 17, we’ll look at how to utilize our understanding of input response and how crows can illuminate the mechanics of membrane behaviour and reveal input response. We might also touch upon the acoustical implications of shaping the oral cavity.

 

Read more about Christopher Millard. Chapter 1 – The Craftsman Chapter 2 – Can you explain how a bassoon reed works? Chapter 3 – Surf’s up! Chapter 4 – The Physicist’s Viewpoint Chapter 5 – The Big :Picture Chapter 6 – We’ll huff and we’ll puff… Chapter 7 – Look Both Ways Chapter 8 – Dialogue Chapter 9 – The Big Bounce Chapter 10 – The Incredible Shrinking Bassoonist Chapter 11 – A Useful Equation  Chapter 12 – Goldilocks’ Dilemma Chapter 13 – Stairway to Heaven  Chapter 14 – Reed MyLips Chapter 15 – Resonance Chapter 16 – Corvids & Cacks Chapter 17 – Lift Chapter18 – Chickens & Eggs Doodles & Design by Nadina

 

 

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