Some short videos on pitch and tone

[uday_shankar]

I made some impromptu videos clips from time to time with a phone camera and posted on social media. Some of them may be relevant to CM, and this post was triggered by the tambura jiva thread (no pun intended !) started by Mr. @thenpaanan .

Here's one on the persistent 7th harmonic (has the characteristics of a flat kaishiki nishada) which is staple to tamburas:

https://youtu.be/5JmK0FFLzdI

Here's one on how singing/playing a perfect chatushruti rishaba, rather than getting lost in a maze of gamakas, enhances the raga experience...this was triggered by a poor chaturshruti rishaba heard from an artist..

https://www.facebook.com/uday.shankar.9 ... jQKqGXe5ul

Here's one trying to show that good tone and pitch goes a long way to enhance the raga experience, even a "core" raga, than a mass of gamaka oriented phrases:

https://www.facebook.com/uday.shankar.9 ... tZ22gFefql

Here's a fun one on the different harmonics (and their swara nomenclature) that can be produced with a good flute pipe:

https://youtu.be/nZdHQOPY_Hg

[thenpaanan]

I made some impromptu videos clips from time to time with a phone camera and posted on social media. Some of them may be relevant to CM, and this post was triggered by the tambura jiva thread (no pun intended !) started by Mr. @thenpaanan .

Here's one on the persistent 7th harmonic (has the characteristics of a flat kaishiki nishada) which is staple to tamburas:

https://youtu.be/5JmK0FFLzdI

Interestingly I find my South Indian tambura often gives me a strong seventh (sometimes it is very annoying) but I don't recall ever hearing it from the Miraj tambura that I had borrowed for some time. As you say it is probably something to do with the physical construction.

Here's one on how singing/playing a perfect chatushruti rishaba, rather than getting lost in a maze of gamakas, enhances the raga experience...this was triggered by a poor chaturshruti rishaba heard from an artist..

https://www.facebook.com/uday.shankar.9 ... jQKqGXe5ul

Indeed. In my experience I have felt this more with instruments than vocal performances. Sometimes a violin will start with a sustained antara gandharam in say kalyani and all of a sudden your hair stands on end and you sit up. But all it was was a "simple" gAndhAram. I think it is some combination of getting the interval perfectly (such as a shuddha rishabham in your demo) and the richness of the tone (i.e. harmonics).

To be sure it is something that does not happen all the time to me in Carnatic music. I would wonder if it was me rather than the sound that causes that effect. Sometimes you are in the listening zone and sometimes you are not.

Voice-wise I would love to create that effect but I don't know if I ever have (no one has ever told me). You get this feeling with o handful of Carnatic vocalists on a consistent basis. I get it more often with Hindustani singers and quite often with select film singers.

Finally, I find that this category of sound (an on-pitch interval with rich but not too much harmonics) music soothes my soul better than all the other kinds of sound. Why I don't know. Movement is essential too but it would be nice to have movement while maintaining this other quality. Western classical music seems to have achieved it somewhat but their interval relationship (equi-tempered) seems to spoil the magic somewhat.

Here's one trying to show that good tone and pitch goes a long way to enhance the raga experience, even a "core" raga, than a mass of gamaka oriented phrases:

https://www.facebook.com/uday.shankar.9 ... tZ22gFefql

Indeed. Unfortunately I can only give one like to this post.

I suppose one of the reasons for the super stardom of some musicians is that they did not shy away from holding a note and displaying good tone as opposed to hiding it by doing a lot of fine-grained filigree work that is the hallmark of today's Carnatic music. To take another example, to my unlearned ears, Ravi Shankar's sitar had better tone than Vilayat Khan's, even though the latter did seemingly more technically sophisticated things.

Here's a fun one on the different harmonics (and their swara nomenclature) that can be produced with a good flute pipe:

https://youtu.be/nZdHQOPY_Hg

Wow. Just by changing the air pressure! One question I have on your chitravenu construction -- why does it have to be a straight tube? What will happen if you have a curved tube like a tuba?

Thanks for a wonderful post (actually multiple posts in one).

-T

[uday_shankar]

Interestingly I find my South Indian tambura often gives me a strong seventh (sometimes it is very annoying) but I don't recall ever hearing it from the Miraj tambura that I had borrowed for some time. As you say it is probably something to do with the physical construction.

It has been my experience also more with Thanjavur tamburas.

Western classical music seems to have achieved it somewhat but their interval relationship (equi-tempered) seems to spoil the magic somewhat.

I agree equal temperament doesn't generate a good feeling of consonance.

a lot of fine-grained filigree work that is the hallmark of today's Carnatic music. To take another example, to my unlearned ears, Ravi Shankar's sitar had better tone than Vilayat Khan's, even though the latter did seemingly more technically sophisticated things.

There is a small passage in the Complete works of Swami Vivekanda which kind of echoes this, more harshly , in a typically Vivekanandaesque way:

In music no more were there the soul-stirring ideas of the ancient Sanskrit music, no more did each note stand, as it were, on its own feet, and produce the marvellous harmony, but each note had lost its individuality. The whole of modern music is a jumble of notes, a confused mass of curves. That is a sign of degradation in music.

The quote is from the following essay:
https://en.wikisource.org/wiki/The_Comp ... _before_us

I suspect the Swamiji must have been refering to HM Khyaal or Dhrupad but perhaps equally applicable to CM where "reproducing gamakaws" has taken center stage over nada. Directly connected is the phenomenon of the proliferation of instruments with no special nada signature such as keyboards, iPads, electric mandolins, as well as devolution of plucked stringed instruments into electronically amplified ones. And of course the deafening sound in sabhas. Rasikas and artists have become so desensitised.

Regarding sitarists, there was Nikihil Bannerjee who sounded better than either of the other two and whose approach was minimalist compared to them.

Wow. Just by changing the air pressure! One question I have on your chitravenu construction -- why does it have to be a straight tube? What will happen if you have a curved tube like a tuba?

More precisely just by changing the blow strength. When we blow the flute, all the air simply escapes into the atmosphere. Nothing "goes through" or goes into the body of the flute and build up pressure or anything like that. All of the blowing action is simply at the blow hole or embouchure. However, in the process, the player creates a vortex near the blow hole, with some of the air escaping off the opposite edge of the blow hole and new air supplied constantly by the player. Roughly speaking, when the rps (rotations per second) of the vortex matches the standing wave frequency (Hertz or cycles per second) of any flute column length (ito a first order of approximation, this is the distance from blow hole to the first open hole, regardless of what other holes subsequent are closed) the flute spontaneously resonates with the sweet sound of the flute. The flute player is constantly and subconsciously adjusting the blow strength as he/she traverses the music. Somewhat harder and subtle is to adjust blow strength for harmonics at the same position, except for the octave harmonic which is a bedrock of flute training and the basis of being able to play taara sthayi (in flute practically same fingering applies for madhya and taara sthayi).

As regards a curved tube, it would work just as well for flute or any other wind instrument. I have made many curved flutes but what recent research by John Coltman and others, which I leveraged, is that sharp bends (miter bends), not just curves, also work if properly compensated for acoustic impedance. I have used one such miter bend, at right angles for chitravenu which is the only way to get the mouthpiece out of the way of the slide. Chitravenu is a L shaped flute and the overhanging portion behind is only a resting place for the slide.

Other than this miter bend, I saw no advantage in any curvature, as it only adds enormously to the headache of being able to cover and uncover and seal a slot with a slide, which is the basis of playing it. Imagine making a curved slide

If there is curiosity in the "action" of the instrument, as well as a peep hole into the tip of the iceberg as to its musical and virtuosic potential, this is a good demo:
https://www.youtube.com/watch?v=TxgAmtSsAmQ

[Vayoo Flute]

Here's a fun one on the different harmonics (and their swara nomenclature) that can be produced with a good flute pipe:

https://youtu.be/nZdHQOPY_Hg
[/quote]

This is something that I showed in the following video - https://www.youtube.com/watch?v=X0iM9Z7LlM8&t=618s.

Testing the higher harmonics in a flute is an excellent way to test the responsiveness of the flute.

[uday_shankar]

Testing the higher harmonics in a flute is an excellent way to test the responsiveness of the flute.

True. Also, the first thing I check when I get a flute is over blowing octave integrity. Then it's a nice warm fuzzy feeling

[uday_shankar]

Testing the higher harmonics in a flute is an excellent way to test the responsiveness of the flute.

Got a nice professional bansuri at F and tested it out, including harmonics. Nice flute.

https://www.facebook.com/738123709/vide ... 663987984/

[Vayoo Flute]

Note that you will always lose a bit of accuracy with the harmonics and one has to adjust accordingly. This is so because the higher harmonics require more forceful breathing and therefore a change in embouchure. Generally, the higher harmonics tend to be over-pitched.

[uday_shankar]

Note that you will always lose a bit of accuracy with the harmonics and one has to adjust accordingly. This is so because the higher harmonics require more forceful breathing and therefore a change in embouchure. Generally, the higher harmonics tend to be over-pitched.

Sure but it all depends on the shruti sensitivity and breath control of the player. Harmonics can be modulated to some degree to be well pitched, as in fact I do unconsciously, all the time and in this video too

[thenpaanan]

Speaking of harmonics and richness of sound, I see that western flautists always use a flute made of some kind of metal, whereas using a metal flute seems anathema in Indian music. I have seen other cultures such as Chinese use different-looking flutes but they also seem to be made of some kind of wood/bamboo. Is this just a matter of tradition or are there specific attributes in the sound quality that they are being selected for?

-T

[uday_shankar]

Speaking of harmonics and richness of sound, I see that western flautists always use a flute made of some kind of metal, whereas using a metal flute seems anathema in Indian music. I have seen other cultures such as Chinese use different-looking flutes but they also seem to be made of some kind of wood/bamboo. Is this just a matter of tradition or are there specific attributes in the sound quality that they are being selected for?

-T

In theory the flute is just a column of air enclosed by the walls of the flute body. So the material should have no effect. However, the wall thickness matters, as the chimney height of both the blow hole and the tone holes matter. Also, the heat conduction properties of the wall matter. Once these variables are eliminated or accounted for, the material of the wall bears no relevance.

It has been well-established through experiments that human prejudice knows no bounds ! In the 70's Dr. Coltman, an engineer at Westinghouse and an amateur flautist, did an experiment with all western subjects , professional flautists, amateurs, lay listeners playing or listening to various flutes whose material was carefully camouflaged. For example a wood flute made to look like silver and a silver flute made to look like wood. The feedback was interesting and completely meaningless... for example the wooden flute was often termed metallic and the silver flute stood out for its deep wooden warmth. If this is the situation in a more objective western setting, one can imagine the situation in India.

@vayoo_flute has been making carbon fiber flutes successfully. They probably are an improvement to the tonality of the bamboo flute. I'll let him speak to that if desired.

I myself make my chitravenu pipes with Aluminum and then have them coated with black teflon,

[thenpaanan]

...
It has been well-established through experiments that human prejudice knows no bounds !

This reminds me of the time I was discussing with a well-known Carnatic musician my initial attempts at learning Western vocal technique and incorporating them in my Carnatic singing. Any other comment like "this is not good" (it was very early in my Western training) would have been acceptable, but what he actually said was "why do you want to mix pasta with uppuma? Those techniques are not applicable to us." I did not remind the musician that he made his livelihood playing Carnatic music on the violin.

-T

[Vayoo Flute]

In spite of what Western experiments might have pointed out, I do think, based on my research, that different materials do have a material impact (sorry for the pun) on the tonal qualities of a flute. I think it is more than just wall thickness, chimney depths and other things that Uday has pointed out. Yes, what makes the flute sing are the standing waves generated inside the hollow of the tube between the blow hole and the first open tone hole. But what drives the standing waves are the vibrating tone hole and the blow hole wall openings. Different wall materials (bamboo vs. metal vs carbon fiber vs plastic) will have different acoustic and vibrating properties - just as drums made of different materials (but with otherwise same dimensions) sound different.

Let us examine what happens during the microseconds before you can hear the note being played on a flute. When a stream of air hits the blowhole edge, the stream gets divided into a part the gets deflected inside the hole and a part that is deflected out into the open air. The split causes the blowhole wall to vibrate. (Try blowing a narrow stream of air on the edge of a paper and move the paper until you can hear a pronounced hiss - here the paper is vibrating just like the blowhole wall). The vibration in the blow hole wall sends shock waves along the length of the tube walls, and the first open tone hole wall also vibrates in sympathy. This sympathetic vibrations between the blow hole and the first open tone hole sets up a resonance and standing waves resulting in the generation of a tone.

Apart from the matter of different materials having different sounds, responsiveness is also a key consideration. This has a lot to do with the time taken for the vibrations in the blow hole to be transmitted to the vibrations in the open tone hole. The distance between blow hole and open tone hole is an obvious consideration - the longer the distance, the slower response time. Hence shorter flutes tend to be more responsive than longer ones. Also the more thick the walls are, the greater the inertia and the longer it takes. Hence thin flutes are more responsive than thick ones. The wall material also matters in the conduction of vibrations from one hole to another. Some materials transmit faster than others - metal and carbon fiber faster than wood and wood faster than plastic.

All of these factors have an impact not only on sound quality but also on consistency between different octaves. I have found that metal and carbon fiber tones produce more consistency in volume and tonal characteristics over the entire frequency range than bamboo. But I do love the bamboo sound in the lowest notes. As with everything in life, it is a question of taste and compromise.

[uday_shankar]

Let us examine what happens during the microseconds before you can hear the note being played on a flute. When a stream of air hits the blowhole edge, the stream gets divided into a part the gets deflected inside the hole and a part that is deflected out into the open air. The split causes the blowhole wall to vibrate. (Try blowing a narrow stream of air on the edge of a paper and move the paper until you can hear a pronounced hiss - here the paper is vibrating just like the blowhole wall). The vibration in the blow hole wall sends shock waves along the length of the tube walls, and the first open tone hole wall also vibrates in sympathy. This sympathetic vibrations between the blow hole and the first open tone hole sets up a resonance and standing waves resulting in the generation of a tone.

Sir I don't think this is the best characterization of what happens, especially the notion of a sympathetic vibration between the blow hole and the first open hole. If this were true chtravenu, which only has an enless narrow slot, should not work ! Please take a look at this video and see that it indeed works. Chitravenu has an L shaped miter bend at mouthpiece and endless slot where holes should be, otherwise it is a flute:

https://youtube.com/shorts/UtK498nslTI

What I have gathered is that yes the air splits at the mouthpiece hole and most of it goes out but it sets up a vortex at the mouthpiece and when the revolutions per second of that vortex matches the open pipe (open at mouthpiece and first open tone hole) standing wave frequency of the pipe length from the blow hole to the first open tone hole the flute spontaneously erupts and stays in vibration. This pipe resonace and the blow act in conjunction without any need for a solid material vibration. The source of "vibrational" stimulus is simply the vortex at the mouthpiece and its interaction with pipe resonance. Hence breath control, to regulate the speed of the jet/vortex is important. This is very different from reed (oboe, nagasvaram) and "lip-reed" (trobone, trumpet, etc). In the latter two cases some material thing vibrates...reed in the case of nagasvaram and lips in the case of trombone. In the case of the flute, there is no need for a material vibration. It is all air.

I do agree that many things can affect the tone and material matters for the subtler effects on tonality, etc.

[uday_shankar]

This is a wonderful introduction to flute acoustics
https://newt.phys.unsw.edu.au/jw/flutea ... 0of%20keys.

[thenpaanan]

(excellent stuff deleted)

The source of "vibrational" stimulus is simply the vortex at the mouthpiece and its interaction with pipe resonance. Hence breath control, to regulate the speed of the jet/vortex is important. This is very different from reed (oboe, nagasvaram) and "lip-reed" (trobone, trumpet, etc). In the latter two cases some material thing vibrates...reed in the case of nagasvaram and lips in the case of trombone. In the case of the flute, there is no need for a material vibration. It is all air.

I do agree that many things can affect the tone and material matters for the subtler effects on tonality, etc.

In all wind instruments, to my uninformed mind, there seem to be two aspects. The first is the mechanism for setting up the standing waves in a variable-sized resonance chamber that give us the sense of pitch and harmonics. As you have explained, the mechanism for creating the waves varies across instruments but the outcome is similar (modulo spectral differences) in terms of standing waves in a pipe.

But how about the second part which is that the energy from these standing waves is absorbed or reflected to some extent by the material of the enclosure. Is it true that different materials such as metal, wood, carbon fiber etc absorb energy differently (spectrally speaking) to a significant extent to cause a difference in the overall tone - sustain, color etc? If so then one could argue that the actual notes heard are different depending on the material of the flute.

Am I talking through my hat here? Perhaps the effect of absorption is not significant to make a difference?

-T

[Vayoo Flute]

Sir I don't think this is the best characterization of what happens, especially the notion of a sympathetic vibration between the blow hole and the first open hole. If this were true chtravenu, which only has an enless narrow slot, should not work ! Please take a look at this video and see that it indeed works. Chitravenu has an L shaped miter bend at mouthpiece and endless slot where holes should be, otherwise it is a flute:

Uday, with all due respects, your chitravenu is NO different to a flute, even though there is a 90deg bend in the air column. I stick to my arguments. The same principles apply to a U-shaped mouthpiece, your L-shaped instruments or a regular transverse flute. Think of our school-days physics class where two people are standing at either end of a long rope and creating a standing wave. You need both of them to create the standing wave. If one end is completely stationary, standing waves can still be created but this will be more like a nadheswaram than a flute. Similarly both open ends of a flute needs to vibrate to create the sound through the tube. In your chitrvenu case, the vibrations are transmitted from the vibrating mouth hole through the L-shaped joint onto where the opening is on the slide. For the vibrations to be properly transmitted across the instrument, the joint needs to obviously be airtight but also be conducive to transmission. If you had used soft rubber for connecting the mouthpiece to the sliding tube, I doubt you would have been happy with the results, as the rubber would have dampened the vibration transmissions.

There are so many ytb channels that compare the sounds of different concert-C flute - flutes made of different metals (silver, gold (various hardness), nickel-silver, copper, etc...) and different woods (African blackwood, rosewood, etc...). All of them have different tonal and response characteristics. Flute material does have an impact and IMO it is due to the parts of the material that vibrate.

[rajeshnat]

There are so many ytb channels that compare the sounds of different concert-C flute - flutes made of different metals (silver, gold (various hardness), nickel-silver, copper, etc...) and different woods (African blackwood, rosewood, etc...). All of them have different tonal and response characteristics. Flute material does have an impact and IMO it is due to the parts of the material that vibrate.

Can you recommend one of them that compares different concerts in YouTube by giving the url.

[uday_shankar]

Uday, with all due respects, your chitravenu is NO different to a flute,

Sir, if you only took care to read my sentence completely (which you even quoted !), you will realize this is precisely what I am also saying !

Think of our school-days physics class where two people are standing at either end of a long rope and creating a standing wave. You need both of them to create the standing wave.

This is a flawed analogy. The only reason you need two people is due to the energy loss. Otherwise the standing wave will sustain due to the reflection from the hard node. Think of a plucked string, where the energy is higher and the rate of dissipation is lower than the people standing with a string and trying to create a low frequency wave... you don't pluck the veena on one side and then pluck it on the other side to sustain the standing wave! You just pluck it once and let it decay. If it is a good vina the sound decays gradually as the energy dissipates. Similarly if the lad holding one end of a rope whose other end is tied to a wall, were all to stand in a vacuum, preferably in zero gravity, he may sustain a standing wave ! You won't need a person at the other end.

If one end is completely stationary, standing waves can still be created but this will be more like a nadheswaram than a flute. Similarly both open ends of a flute needs to vibrate to create the sound through the tube. In your chitrvenu case, the vibrations are transmitted from the vibrating mouth hole through the L-shaped joint onto where the opening is on the slide. For the vibrations to be properly transmitted across the instrument, the joint needs to obviously be airtight but also be conducive to transmission. If you had used soft rubber for connecting the mouthpiece to the sliding tube, I doubt you would have been happy with the results, as the rubber would have dampened the vibration transmissions.

Sir, these are flawed characterizations, I don't even know where to begin, Think of the open pipe experiment where a pipe is clamped to a holder and open at both ends. The moment you bring an excited tuning fork of the correct frequency at one end, the pipe resonates. There are no tuning forks at the other end needed. This happens regardless of the thickness of the pipe wall, the material of the pipe, the damping agents at either end, whatever. There is a small detail called end correction which depends only on the internal diameter of the pipe. The propagation of standing waves through a pipe, open (i.e. open at both ends) or closed (i.e., closed at one end) are extremely well explained via animations in the website linked above. I urge you to take a look. The only difference between open and closed pipe is that the closed end will always be a pressure anti node (and consequently a displacement/motion node) while the open pipe both ends are always pressure nodes (and consequently a displacement / motion antinode . This automatically results in the absence of all even harmonics in a closed pipe. Other than that both need stimulus only at one end. I highly recommend the following website where a good explanation of the differences between the two
https://www.phys.unsw.edu.au/jw/flutes.v.clarinets.html

Whatever be the case, you are entitled to your characterizations and I don't wish to prolong any arguments for want of time or energy.

@thenpaanan, the propagation of sound through air is a quasi-adiabatic process, i.e., it is almost loss free. Hence we are able to hear each other across a football field as the sound travels without losing much energy. If you look at the thermodynamics, the gamma value is around 1.3 in constant PV to the power gamma. For a completely adiabatic system it will be 1.4 and for a completely isothermal system (that which dissipates energy to the surroundings) it will be 1. However, within an air column, the situation is different. There is rapid dissipation of energy as you move closer to the walls. This happens regardless of the materials of the wall. So I am unable to comment deeply on the wall material effects. This article from Dr. Coltman is very good:
https://pubs.aip.org/physicstoday/artic ... a-positive

[Vayoo Flute]

Cutting out all of Uday's actual science and my "pseudo-science", I still maintain that flute material does have an impact on tonal quality and this must have something to do with the material itself vibrating - so pronounced at the blow hole and the first open tone hole. I also do not want to waste more of others' time on this.

[uday_shankar]

Cutting out all of Uday's actual science and my "pseudo-science", I still maintain that flute material does have an impact on tonal quality and this must have something to do with the material itself vibrating - so pronounced at the blow hole and the first open tone hole. I also do not want to waste more of others' time on this.

I agree 100% with this sir. These are secondary effects and practical problems which are the most important problems to be tackled by any designer/maker of instruments.

I even think the thin-walled silver Boehm flute which is the standard western flute, should have serious problems due to the vibration of the body itself. The only reason it doesn't seem to, is perhaps because the player holds it in his/her hands thus damping/preventing vibration. Should we find a way to suspend the Boehm flute at the ends by thin wires and get someone to play, the tonal effect would be completely different due to the vibration of the body. This is just speculation on my part based on my experience with aluminum extrusion pipes and trying to reduce their weight by milling at the outside. At some stage the whole flute was vibrating. I have similar issues with extra light slide, which is an advantage in terms of playability but vibration is a bugbear. It causes a flutter which jinxes the sound. A proper sealant mixture of propylene glycol and hydrogen peroxide provides the optimal viscosity to arrest the vibration 99% of the time and I carry on precariously. We have to keep going with whatever we have

[Vayoo Flute]

If the material is not vibrating, we may have a sound that is closer to a purer sine wave and with fewer harmonics. This will make the sound more boring. As with everything this is probably a question of compromise - not too much vibration but enough to create some colour to the tone.

[thenpaanan]

If the material is not vibrating, we may have a sound that is closer to a purer sine wave and with fewer harmonics. This will make the sound more boring. As with everything this is probably a question of compromise - not too much vibration but enough to create some colour to the tone.

Indeed. A tuning fork is most definitely not a musical instrument. A good example is the tiny flute that is used in the background when depicting rustic or wild mountain scenes. The raspy sound (and other non-harmonic sounds) are integral to the charm of the sound. Even bagpipes -- I used to be irritated with the non-harmonic mix in the sound when I first listened to it, but now I kind of like it. The color of the tone (or harmonic mix) even when it is to the detriment of pitch clarity is what lends it identity it seems.

-T

[uday_shankar]

If the material is not vibrating, we may have a sound that is closer to a purer sine wave and with fewer harmonics. This will make the sound more boring. As with everything this is probably a question of compromise - not too much vibration but enough to create some colour to the tone.

Interesting thought/hypothesis. Indeed the flute waveform, especially for soft blowing of the fundamental, is quite simple and quasi sinusoidal. I personally dislike "features" I cannot control such as the vibration of material parts. A controllable way to introduce harmonic richness in the sound of the flute is by modulating the blow, given other features of the flute that make such modulation possible. So a simple "pure" blow can be modified to a breathy/raspy blow. Pandit Hariprasad Chaurasia, the bansuri legend, used to have a "pure" blow until the 1980's and it was sweet. Many memorable recordings from that era are with the pure blow. Then he gradually changed to a breathy/raspy blow, which are even more memorable. In south Indian/ Carnatic circles such a blow would be sophomorically classified as "saar avar romba kaathu oodaraar". But such breathy blowing is the life blood of bansuri and in fact south Indian flute too.

[Vayoo Flute]

Interesting thought/hypothesis. Indeed the flute waveform, especially for soft blowing of the fundamental, is quite simple and quasi sinusoidal. I personally dislike "features" I cannot control such as the vibration of material parts. A controllable way to introduce harmonic richness in the sound of the flute is by modulating the blow, given other features of the flute that make such modulation possible. So a simple "pure" blow can be modified to a breathy/raspy blow. Pandit Hariprasad Chaurasia, the bansuri legend, used to have a "pure" blow until the 1980's and it was sweet. Many memorable recordings from that era are with the pure blow. Then he gradually changed to a breathy/raspy blow, which are even more memorable. In south Indian/ Carnatic circles such a blow would be sophomorically classified as "saar avar romba kaathu oodaraar". But such breathy blowing is the life blood of bansuri and in fact south Indian flute too.

Thick-walled flutes tend to vibrate less and therefore may be more "pure" as you put it. In fact, if you look at the early videos of Hariprasadji, he seems to be using a thicker walled flute, much like the Kerala bamboos, rather than the ones from Assam that are mainly used for the current thin-walled bansuris.

Whether one likes a breathy blow or not is a matter of personal taste. Certainly the airy, breathy blowing from a quena or shakuhachi player sounds very nice, but this type of music is often associated with natural surroundings of mountains, forests and winds. So the hissing you hear seems an important part of what the music represents. When it comes to rendering a Carnatic composition, I don't like any hisses. Even with Hindustani raags on longer bansuris I only like breathy notes used in a limited way and only in some places. Maybe I am too "old-school".