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Thread: Spectrograms...

  1. #1
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    Default Spectrograms...

    ...Why don't we use them to illustrate how different types of wood sound?

    I know that no two ukes are the same but this technique is used to analyse things as complex as the human voice, so it would definitely help a lot in terms of describing spectral qualities of say koa vs. mahogany vs. spruce woods to the untrained ear. Just using words such as warm, mellow, bright or crisp make it difficult for beginners to grasp what that actually corresponds to in terms of sound, unless one already has experience hearing the differences.

    You'd be able to visualise that one is stronger on mid-lows, another one on highs hences brighter, one has more sustain etc. If someone made a reference table of spectrograms of various types of standard woods in identical lab conditions or if makers made "for reference only" ones for each of their models, it would probably help people get an idea of the differences among the various woods. Even better, one could add a vibrometer scan to visualise how the uke resonates to say G, C, E and A.

    Do you reckon?

  2. #2
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    Actually, the human ear is capable of hearing more subtle differences in the character of sounds than can reasonably be displayed by a spectrum analyzer (unless there are some incredibly capable analyzers far more capable than the stuff I've worked with).

    A trained human ear can hear down to 1-cent or less across approximately 20hz to 18 or 20khz. Getting that degree of precision out of hardware or FFT software would require a huge FFT matrix and very fast sampling - even today's computers wouldn't be able to process it in anywhere near real time - or even reasonable time.

    In fact, I'm not sure you could reasonably display the information in a visual format that would be meaningful.

    John
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    True that the human ear is much more precise when you're listening to the uke in the flesh, there's nothing better than trying a uke directly. But when you can't and you have to listen to comparisons or reviews on youtube for example, you hear the sound through a long chain of audio devices and acoustic factors that will deteriorate the sound and affect how you hear it. You won't be experiencing the intensity nor directional properties of the sound it projects either etc.

    With spectrograms and vibrometer scans you get reliable and immediate images of the frequency response through time to a stimuli, which can nicely complement an audio recording, and with very little equipment needed. People use them all the time to analyse other types of music instrument acoustics and other audio signals, it's an established method. Many years ago I worked in an acoustic research lab that used them a lot, although I wasn't working with them myself (I've changed field since then). I remembered about it today when I was trying to hear the difference between ukes made of different woods on youtube. Kept thinking: "that's nice but if only I could just see a spectrogram / vibrometer scan, I'd get a better sense of the actual acoustic properties of that wood / uke and I'd be able to really compare them objectively"

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    Default

    I'm also curious about this, and have a suggestion for how to measure the response.

    In the speaker building community, there is a lot of attention paid to response measurement and some useful software tools that could be applied to measuring the response of ukuleles with different build characteristics.

    For example, this software provides a variety of spectrum visualization tools and is free: http://www.hometheatershack.com/roomeq/

    It's important to isolate room resonances from any measurement, and to use a calibrated mic.

    I've also been curious about visualizing the physical vibration patterns on the top of a uke using a strobe light. Like this sort of experiment, but with a uke: http://youtu.be/q4setd7BZWM?t=37m53s

    My guess is that there is a lot to be learned about bridge and brace design as well as the general resonance patterns of different tone woods.

  5. #5
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    Hi

    I think the most serious problem is that our language (and aural psychology) does not correlate to the frequency spectrum. We say something like "this ukulele sounds warm" but I have not seen a consensus as to what frequency does that to our ears.

    In addition, the time domain information (eg, attack, rise and decay etc) will be lost in Fourier transform. The phase information is usually lost (unless you do sine and cosine spectrum analysis).

    And to get a really good recording is remarkably hard.

    Cheers
    Chief

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    Indeed, it is really difficult to describe tonal quality and also very hard to make a faithful recording, especially with non professional equipment. So I salute the effort put into this by all the people who are doing online videos and thank them for sharing their super valuable knowledge with the rest of us.

    Maybe the manufacturers - who can afford renting anechoic rooms and using pro-level microphones - could use these techniques to add the imagery to their spec list? (I'm just brainstorming out loud hehe)

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    Maybe there's a master's thesis in acoustics waiting to be written about this... "Correlating perceived tonal response of different ukulele woods to their spectral analysis: a mapping of the psychoacoustic perception of warmth and brightness in small wooden string music instruments" lol

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    Quote Originally Posted by Lalou View Post
    Maybe there's a master's thesis in acoustics waiting to be written about this...
    Well, I bet there have been many many attempts. This sure sounds like a graveyard for a graduate student, and that for a PhD thesis. And I am sure everyone in the audio/sound/recording industry is working on this.

    Cheers
    Chief

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    I meant specifically for the ukulele... Haven't seen much work on this area, people in acoustic research tend to work on guitars and violins and such

  10. #10
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    But wouldn't the tonal response of the wood be totally subjective, based on thickness, grain, and bracing used? Not to mention finish, strings, bridge, saddle, nut, style of string attachment, and method of attack (plucking vs. strumming, nails vs. flesh)?

    Maybe that's why no one has quantified anything yet - there are too many variables, even within a single type of instrument wood. Speakers would be easier, especially if a standard existed for thickness and finish.


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