Other web Sites
Harmonica Blues  Harmonica Amps
Harmonica Links Harmonica Pages
• Archives Home
• Years
 · 1992
 · 1993
 · 1994
 · 1995
 · 1996
 · 1997 		 · 1998
 · 1999
 · 2000
 · 2001
 · 2002
 · 2003
 
Web HarpL
Ebay Searches:
Amps:
Microphones:
Effects:
Harmonicas and Gear:
Harmonica Music and Instruction:

 

 

Harp-L Archives

[Previous Message] [Next Message]
[Previous in Thread] [Next in Thread]
[Start of Thread] [End of Thread]

From: Mike Curtis
Date: Tue, 3 Dec 1996 12:20:46 -0800 (PST)
Subject: Re: oscilloscopes, etc.

On Tue, 3 Dec 1996, Pat Missin wrote:

> For a start, I think Mike Curtis should be applauded for doing some hands-on
> experiments and I hope other harp-lers will feel inspired to have a go
> themselves. Mike as an electrical engineer will have access (I presume) to
> good a quality 'scope, but most of you reading this will have some form of
> sound software, using 'scopes or spectrum dislays. Also there is an
> excellent piece of freeware (yup - it's free!!) for PC called Scoper, which
> contains a basic realtime oscilloscope and spectrum display. Most shareware
> houses should have it.

Actually, for this purpose any oscilloscope capable of triggered sweep
will work just fine. This includes just about every oscilloscope ever
manufactured (although I also have an old cheapie that doesn't have
triggered sweep - anyone wanna buy a piece of garbag.... - I mean - a fine
old Heathkit IO-4560 really cheap ;-) I'm sure the PC versions will work
just fine, as long as they respond to significant overtones up to around
10 kHz, and have enough definition. Audio is a piece of cake. Radio
frequencies present a far greater challenge for a 'scope.

Also, assuming it works like a traditional spectrum analyzer, the spectrum
display in Scoper would probably be really handy for analyzing harmonic
content. Instead of having to do waveform analysis (or guesstimate if
you're basically lazy like me :-), just look at the display and it tells
you exactly what's there and what's not.

> Having thus praised Mike, I now set about undermining his conclusions, but,
> as a trained electrical engineer, Mike could well know more about the use of
> oscilloscopes than myself.

I hate to take all the romance and mistique out of it, but the use of the
oscilloscope is stupid-simple. Just connect it to the device you wish to
measure; in my case, a microphone. Select a time per division setting
that is suitable, which I did by playing a note then turning the selector
so I could see about three full waveforms on the screen. Set volts/div
likewise, so the waveform fills the screen at max, but doesn't go outside
the display. You may have to diddle the trigger level to stabilize the
display.

> I honestly hope he will correct any mistakes I
> might make here. He also pointed out that the choice of the two harps he
> compared was dictated by only having one wooden body harp handy - I have the
> advantage of a workshop full of harp odds and ends.
>
> Mike compares a Hohner Blues Harp in E and a valved Lee Oskar in Eb and
> finds that they produce different oscilloscope traces. I'm not at all
> surprised - my ears tell me that a Blues Harp has a different tone to a Lee
> Oskar. The conclusion that this proves an inherent tonal difference between
> wooden and plastic bodied harps, however, I do not go along with.

Actually, I covered myself here. I said it could be any of a number of
things. I realize the reeds and everything else are probably different.
but it's all I had.

Also, I pointed out that there was virtually no difference when playing
with both resonant mouth and hands. There was little difference with
resonant mouth. With no hand cup and mouth nonresonant (I let air
escape), there was a great difference, both audible and on the 'scope.

The one conclusion I reached is that the most difference between these two
particular harmonicas would be noticed by the players with the least
resonance, and the least difference would be from players with "double
resonance", which produced an almost perfect and identical sine wave from
both.

A side thought on "resonant bending" - we all acknowledge that resonance
results in greatly increased volume. Players using what I define as
"nonresonant bending" (requiring both reeds, or the opening reed) have
severe problems with feedback under conditions that "resonant bending"
players do not. This is due to "resonant" players having a much louder
"acoustic"" sound than "nonresonant" players. With something around 15 to
20 dB more raw harp sound, it's not too hard to figure out why :-)

> There are
> many differences between the Blues Harp (I assume that is is one of the Hand
> Made jobs, as Mike said it was an old harp)

Yes I believe it's handmade. It's not MS.

> and the Lee Oskar. Yes, the BH
> has a wooden comb (pear wood, I believe) and the LO a plastic one. However,
> the chambers in the two harps are of different capacities and shapes, the
> cover plates are of a different design, the type of brass used in the reeds
> and reedplates is different and (most significantly of all, in my opinion)
> the reeds are very different dimensions. Any one of these could equally be
> the reason for any difference in tonal output. Why decide that it is the
> body material that makes the difference?

I don't think that, but I'm not ruling it out, either. But what I proved
is that the particular technique used can either make them sound vastly
different or (virtually) exactly the same.

> Also, Mike says that the addition of valves does not make a great difference
> to the tone. Well, is that the case? If so, how do you all tell the sound of
> a chromatic from the sound of a blues harp?

Valves on a partially valved diatonic affect only blow 1-6 and draw 7-10.
My test involved both blow and draw. I saw no significant difference in
waveform due to valved or unvalved.

Also, even when I play unvalved, it sounds very much like chromatic. I
frequently have visiting harmonicists remarking along the lines that they
think I'm playing a chromatic (e.g. "I play a small harmonica", etc.) The
pickup I use is a large chromed tube (the shell of an old Guyatone harp
mic), which is more chromatic sized. But the main thing is the music. I
get the "missing" notes, and I get a tone that's very chromatic-like,
whether I use valved or unvalved diatonics.

Because both test harps were valved, it would have the same effect on
both, and cancels out algebraically.

> Another thing to bear in mind - the tuning of the harps is probably
> different. A Blues Harp tends towards just intonation, the Lee Oskar towards
> equal temperament. On any instrument a 12TET chord will sound
> rougher/harsher than the same chord in JI, due to the inharmonic combination
> tones caused by the temperament. The harmonica is especially prone to these
> combination tones.

True, but I tested only single notes, so tuning should have no effect,
unless there were a slight ringing effect, and even that would not be a
significant factor as a function of micro-frequency. The fact that one was
E and the other Eb would IMHO have a far greater impact. Testing chords
on a 'scope would be meaningless in this context.

Also, Lee Oskars aren't equal tuned. I can dig out the exact tuning specs
if need be (Where is Danny when we need him :-). I believe (by ear) that
they're a bit closer to equal temperament than some of the Hohners, but
the overall "feel" I get is just intonation. The only truly equal tuned
diatonic I know of is the Golden Melody, which is audibly discernable
as equal tuned.

> Anyway, Mike's quick try-out made me try a more balanced experiment.

Which is exactly what I hoped would happen. I tossed this out to
hopefully quiet speculation and get some hard tried and true facts.



This raises a very interesting point. In my experience, the best players
say there's no big difference between harps. Beginners notice a HUGE
difference. I find my harps all sound pretty much the same. My findings,
that the more resonance, the more sinusoidal the waveforms became, support
this.


-- IronMan Mike Curtis
New Cassette available - email for details