harmonic content of acoustic guitar.

[Steenamaroo]

hey all.

not sure if this should go here or not, so please feel free to move it.

i'm thinking ahead to studying next year and trying to half plan what i want to do in my head. i'm doing a music production degree and will have to write a dissertation on an area of my choosing.
I've thought about investigating use of a few different microphone types and several microphone positions when recording acoustic guitar,
and how these factors relate to the harmonic content recorded when playing each pitch.

basically, i guess the idea is to 'prove' that a certain mic pointed a certain way, at a certain distance,is the most accurate representation of that particular instrument (within my own research).


the problem that i can't understand is, what would be the benchmark?
every instrument has different tonal qualities, and therefore different harmonic content right? so, what would be an acceptable scientific way of saying "this is how the guitar sounds, and as such, this is what we are aiming to get close to"?

hope that question makes sense!

thanks.

 

[miroslav]

How about a live demonstration?

Writing about sound is fine...but I think people "get it" much faster if they can actually hear it.

 

[moresound]

How about a live demonstration?

Writing about sound is fine...but I think people "get it" much faster if they can actually hear it.

This sounds like a great idea write up a paper then give a live demo to show your findings! .....could end up acing the course with intuitiveness.

 

[Steenamaroo]

thanks guys.

i'm not sure there'll be an opportunity for live demonstration, but there'll be audio and visual evidence of every recording included with the written work,,

but the problem is

if i say for example, an sm81 more accurately portrays the instrument, than an re20,they're going to say, ' how do you know'?

i mean, sure you use your ears and everyone will know which mic/placement sounds best, but i'm gonna have to prove how accurate the recording has been, by comparing to some kind of factual resource about, or measurement of guitar tone/harmonics.

what would that resource be?

 

[NYMorningstar]

hey all.

I've thought about investigating use of a few different microphone types and several microphone positions when recording acoustic guitar,
and how these factors relate to the harmonic content recorded when playing each pitch.

basically, i guess the idea is to 'prove' that a certain mic pointed a certain way, at a certain distance,is the most accurate representation of that particular instrument (within my own research).

the problem that i can't understand is, what would be the benchmark?
every instrument has different tonal qualities, and therefore different harmonic content right? so, what would be an acceptable scientific way of saying "this is how the guitar sounds, and as such, this is what we are aiming to get close to"?

hope that question makes sense!

thanks.

The question makes sense but there is no one answer for it. It's always going to depend on other factors which are always different and flexible depending on the instruments, the song, the artists and the experience and preferences of the audio engineer. Benchmarks are either non existent or fade into oblivion real fast in this field.

A good source is the most important factor in capturing a good sound. To get a good sound out of an acoustic instrument you have to include the next most important factor, the effects of the sound by the environment (the room). The most accurate represention of an instrument may not be the best sound you can record.

You want to have a good balance between the instrument, the room and the tonal qualities of the mic. The mic will have different qualities too based on it's on axis or off axis and it will also be affected by the mic preamp.

Well I've taken enough of your time and everyone elses. Good luck with your research!

 

[Steenamaroo]

damn.

thanks NYms, although that's a great answer, i'll admit it's not what i wanted to hear!! hehe

i mean, i'm aware that room/preamp/instrument/musician, heck even humidity will all have an effect on the sound, but i was kinda hopin i could put most of them down as being constant and ignore them.

i'm probably asking too much too soon anyway. i'll wait till i get there and suss it out further.


havin said that (thinking out loud), i could change the topic slightly. maybe from the viewpoint of comparing the mics against eachother, rather than focusing on how accurate / true to the source they are.

ah well,,food for thought guys! thanks.

<edit> just noticed you said song. not nitpicking at all, but so people know, i'd probably just take recordings of each pitch on the guitar. possibly individual chords too...idk, haven't thought that far yet.

 

[DrewPeterson7]

havin said that (thinking out loud), i could change the topic slightly. maybe from the viewpoint of comparing the mics against eachother, rather than focusing on how accurate / true to the source they are.

I think that makes the most sense - the only alternative for a 'benchmark' recording I can think of would be reference mics in an anechoic space, and then comparing them to various mics in various positions in the same space, but of course the space is part of the point, with certain mic techniques...

I'd say your best bet is to get into a good acoustic space, or rather several, and carefully reconstructing the test in several rooms with several mics in several positions, and see if you can draw meaningful conclusions about how a particular approach will emphasize a particular harmonic range. If so, then it'd give you a bit of a reference based on what you were looking for, for a particular song.

Interesting idea, anyhow. You may very well conclude that you can't generalize, and that harmonic content is more room-sensitive than mic position-sensitive, but even that is a valid and useful result.

 

[Steenamaroo]

thanks Drew! we're getting somewhere now!!

so if there's a notable difference due to mic choice, i can research and explain why, and if there isn't, i can research and explain why other factors like room acoustics are so influential!


i think that's probably the best plan, so mission accomplished! now i can spend time researching microphone and instrument construction and acoustics in advance, rather than panicking about this when time is running out!

thanks guys.

 

[mattdee1]

Hate to be a wet blanket, but I think your project sounds pretty ambitious.

On the one hand, if you want to gauge "microphone accuracy", you need some sort of objective standard to measure against. In other words, you need to know how to quantify exactly what is being reproduced before you can quantify how well it is being reproduced.

If you start getting into simply "what sounds best" then you've moved from objective standards to subjective ones, and those will differ from person to person.

For what it's worth, in the field of Noise, Vibrations, and Harshness (NVH)--at least in the automotive sector--the gap between subjectivity and objectivity is usually bridged by the use of "juries" of people who rank how things sound and feel using some standardized scale, and then the numbers are tallied up and trends are extracted. It's actually a lot more complicated than that, but that's a view of it from 30,000 feet.

 

[dintymoore]

... the only alternative for a 'benchmark' recording I can think of would be reference mics in an anechoic space...

Yes, but this whole thing is a "university thinking" concept and has little, if any value in music.

All mics flavor the sound of a recording and the thought that what you want is to capture the real sound as accurately as possible is scientifically valid but musically has nothing to do with anything.

It sounds like the "university thinking" I have been trying to get as far as I possibly can get away from all my life.

In the end it proves nothing. Who cares? Good recordings aren't made in anechoic chambers with reference mics. If you want a great acoustic guitar sound, just set up two Neumann KM84's - that's the musical sound. Then you have a marriage between mic and guitar, which is how all music recording is done.

To me the whole idea is not that original or really anything that would make me want to do it or see the results. In the land of "so what?". It's all been done before.

 

[The Cancers]

This might be way off base.
But I'm sitting here trying to consider how you might scientifically approach the concept of accuracy in mic placement and selection.

I guess the ideal mic choice and placement would be indistinguishable from the actual instrument being played in the room, when played back on a full range, uncolored playback system.

So here's my thought.

You set up a measurement mic that's going to record everything you do.
This sucker's gonna be about five feet back (maybe closer, maybe further, just far enough that it's out of the near field - here I'm assuming that your experiments with position will be in the near field) and so recording (approximately) the sound of the instrument in the room.
You need an SPL meter at the same position as the mic.

You do your test recordings.
Record a short phrase, chords, whatever you want, with various mics and positions, each time keeping detailed records and making sure you keep your measurement mic files associated with your close mic files (I'd do it by just setting up two tracks for recording in whatever DAW, one is the experimental track, one is the control. The control always records what the measurement mic hears, the experimental gets the mics you are experimenting with. Most DAWs have facilities for making markers and notes and whatnot, so it shouldn't be too tough to keep it all arranged). You'll likely need help here, as you're gonna be using your SPL meter to measure and record (as accurately as possible) how loud the guitar in the room actually is.

Alright, now once you've done all your test recordings, you go find yourself the most accurate near field monitor you can find (my assumption up until now has been that you were doing this all in mono. If it's stereo placement you're working on, then you can probably figure out what would need adjusting).
You have your detailed records of the SPLs of your various takes at the measurement microphone, right?
You are gonna place the monitor as close as you can to the spot where the guitar was (I'd centralize it at the soundhole, though you might have a better idea where the sound projects from than I do) and use it to playback your experimental recordings.
Use the SPL meter to ensure that the playback through the monitor is as close as possible to how loud the actual guitar in the room was.
Now playback your experimental recordings and record them through the measurement mic again, this time on a third track.
Once this is done, you'll probably need to do a little bit of time aligning (due to latency introduced by the process of D/A conversion, sound transmission through the air then another round of A/D conversion) of this new measurement mic track with the original measurement mic tracks.

Now, if you play the original measurement mic tracks against the new ones, with the phase flipped on one of the tracks, there should be some significant frequency cancellation.
Your ideal mic in the ideal position would yield complete cancellation (though that's gonna be impossible), but whatever particular mic/position gets you closest to zero is gonna be the one that most closely/accurately matches the original source.

As I typed this, I thought of a million things that could introduce inconsistencies into the experiment.
I tried to keep it as simple as possible and introduce as few variables as possible.
Some things to keep in mind:
It's gonna be absolutely critical that the measurement mic and spl meter don't move at all throughout the duration of the test (and now that I think about it, you could probably skip the spl meter and just use your DAW's metering of the input from the measurement mic to perform the same function). Same goes for any furniture or other crap in the room. It might even be worth it for you (or your test guitar player) to sit in the same spot (as during the original recording) with the monitor in your (his/her) lap during the playback section of the testing, as I could see everything in the room affecting what the measurement mic hears.

It's gonna be mighty hard to capture the exact sound of the guitar in the room with just one mic in the near field.
This might mean either doing stereo recording or moving out of the nearfield for your experimental positions. Both of these options are gonna introduce more variables and inconsistencies.

I dunno. There's a lot more wrong here (probably most glaringly the fact that the experiment I just designed could be done by someone who is deaf - probably not ideal when you're dealing with sound) than there is right. But it's an idea and maybe a jumping off point.

Please let me know if you like it, have any thoughts, or just didn't understand anything I put in there.

 

[Steenamaroo]

no probs on the wet blanket front. i appreciate your input..but..

In other words, you need to know how to quantify exactly what is being reproduced before you can quantify how well it is being reproduced.

this is exactly the question i came here asking.

If you start getting into simply "what sounds best" then you've moved from objective standards to subjective ones, and those will differ from person to person.

at no point will i be getting in to good, better or best. preference and opinion aren't meant to be a part of this.

the options are either to see which microphone is most accurate, in relation to some kinda of preexisting measurement (which we've established doesn't really exist)

or, to compare the response of some microphones, with the aim of understanding why they each have different characteristics, if indeed they do.



in response to dinty, to paraphrase, you're saying it's all been done before, and it's pointless.
that may be true, but i duno if that's a criticism of me, or of the way universities seem to work.

To be clear, i don't think this is some immensely interesting and pioneering area of research,lol... i think it's a possible way to bang out a decent dissertation, and learn something whilst doing it.

 

[Steenamaroo]

@ cancers, thanks for the response! i appreciate the time you took there.

that all completely made sense, and it's all worth keeping in mind.

The only thing that concerns me is, maybe it's an overly elaborate way to do something that maybe wasn't that great an idea from the start! lol

unless there's more input, i'm really starting to think that directly comparing a few mics, and drawing conclusions about the influence of their design and construction on their freq response, might be the way forward.

 

[dintymoore]

... Please let me know if you like it, have any thoughts, or just didn't understand anything I put in there.

I'll bet the scientists at EV or JBL have spent years doing this sort of thing.

What I ask is - why? Who cares? Do you want to be a scientist or a musician?

Because if you want to be a musician, it's all signed sealed and delivered - you just set up two KM84's and press record. Whatever room and speakers you play it back on will affect the sound.

The musical way is to accept that the mic, room and speakers will affect the sound and work with that.

I swear whenever you take the "song" out of an equation and start thinking like this, things get stupid and I ask "why are you doing this?". It's all been done over and over and over and who cares? It's not musical.

Besides, music isn't even about sound, it's about feel.

 

[Steenamaroo]

seriously dinty, i get what you're saying.
trust me, this isn't the sort of thing i'd be doing outside of study.

 

[dintymoore]

seriously dinty, i get what you're saying.
trust me, this isn't the sort of thing i'd be doing outside of studying.

What's the final goal? And how do you answer the question "so what?" as applied to that goal?

 

[DrewPeterson7]

Yes, but this whole thing is a "university thinking" concept and has little, if any value in music.

All mics flavor the sound of a recording and the thought that what you want is to capture the real sound as accurately as possible is scientifically valid but musically has nothing to do with anything.

On one level I don't disagree, at all.

However, I do think that this could be musically valid. Again, if the focus is not on accuracy in an absolute sense (I mean, there's a reason most of us don't use reference mics when recording), but rather on which approach emphasises which frequencies, then it's just a good way to quantify how a particular approach could bring out or minimize a certain frequency range. For example, if you know that a particular micing technique tends to emphasize the 400hz and 1.4khz region with a bit of attenuation around 8khz, then that might be a good approach for a song where not much is going on in these regions but if you've got a vocalist with a lot going on in the 1.4 range then you'd want to try something else. You could do this trial-and-error, or you could do it for a decade or two until you know this kind of inuitively, and that'd work... But, if you can demonstrate that this is a scientifically repeatable phenomina, then the learning curve is a lot faster.

Think of it as something like proximity effect. We know it happens, we know why, and it's repeatable. We can use it much more effectively while recording because we know it's going on than we can by just blindly trusting our ears and futzing around until we get a sound that works. It's more efficient, which means faster, easier, and ultimately better results.

Besides, if it's FOR a university, well, it's a great way to get credit.

 

[Steenamaroo]

the final goal is to complete a degree course dude.lol.

but really, it's about learning something useful. maybe the whole 'most accurate mic' thing wasn't that useful,
but like drew was saying, i think it's important to know how the microphones in your collection differ. (which is why i think i'll study/write about it)

if i compare a load of mics and learn that one has certain characteristics and an other has the opposite, i like to think i'll remember that and use that knowledge in future.

kinda like, i know if i want to capture extremely low bass, out of my collection, i'm gonna reach for a d112 or somethin, cos a 635a just wont get it. It's also nice to know that an sm81 might capture the same bass, but sound more defined and tighter than the 112?

what's wrong with taking that a bit further?

 

[dintymoore]

I guess what I'm saying is that there's so many interesting things you could spend time on and this just isn't one of them.

Is the Plastic Era near over and what's the next one? Why does plastic vibration make us sick and wood make us relax? Are cancers related to the Plastic Era? Does the harmonic content of cymbals above 100KHz affect us? What is the scientific basic for the different psychoacoustic reactions of a 50's K Zildjian compared to a shiny new Paiste cymbal and do babies react to that? Will Samuel Carey's growing earth concept have musical implications when it's finally accepted? Is song form based on the sex act? Why does Eb sound warm and B natural sound "pointed and sharp" regardless of what instrument, eq or octave? Does the earth resonance change when the light changes with the seasons? What is the relationship between fish swimming in schools being able to make right angles in unison and musicians jamming? Why do we want the V chord to resolve to the l chord?

To me that's interesting stuff that I wonder about constantly, what we were talking about before is old and even if you did it, in the end... so what? There's no promise that I can see you'd net any real world gain.

 

[Steenamaroo]

well,,,i can't say i disagree with you,

but I've considered this topic cos it's within my means, it's realistic, it's related to what I'm interested in, and i hope to learn from it.

i can completely see why someone would disapprove and say that this idea isn't strictly musical, or related to music, but at the same time it's not meant to be.


idk, i'll think some more about it, cos it would be interesting to pick a topic that's more 'real world useful', but lets face it, that's not gona be what an examining board care about.



while i am agreeing with you in general, i don't think you can say this isn't interesting full stop.
that completely depends on who you are and what you do.
This kind of thing may have been incredibly interesting and useful to M.Joly or MShilarious when they were my age or younger.
then again, i could be completely wrong about that.
you yourself mentioned EV and JBL doing that kind of thing. It's not the case, but what if this was something i really enjoyed, and designing speakers/microphones for electrovoice was exactly what i wanted to do in life?

anyway, cheers for the input.
it hasn't gone ignored!