When you play two different notes at the same time, your ear hears the two notes that you play, and a third note, which is made up of the difference between the two notes that you're playing. This note is called the 'difference tone'. Difference tones are not unique to the harmonica - they're part of the way your ear hears sounds. Normally, the difference tones are pretty subtle. They're nowhere near as loud the notes that generate them, so they're very hard to hear.

However, certain mikes, (especially Shure Green Bullets) and certain amps (especially old Fender tube amps) really make them stand out. Since these are the very mikes and amps used by many harp players, difference tones are an important part of "that" sound that's so closely associated with Chicago-style blues harp.

Most of the time, you don't want to emphasize the difference tones, because they sound harsh and dissonant. They won't ordinarily fit in with the chord that you're trying to play. But some of the best harp players have learned to use them to their advantage. The thing that makes them interesting is the way they behave when you bend the notes that you're playing. Perhaps the best way to understand difference tones is to listen to an example.

Click here to download an MP3 file that contains a short fragment from the Siegel-Schwall band's recording of Jimmy Reed's blues classic, "Hush Hush". (This performance appeared on their album entitled, "The Siegel-Schwall Band" - which is not currently available on CD). The harp player is the great Corky Siegel. Listen to when he does with difference tones (about 25 seconds into this sample). And listen to the audience's reaction when Corky seems to play a chord, and bend one note up while simultaneously bending the next note down. The effect is pretty startling…

From: David Fairweather BlindOwl@InReach.Com
Date: Wed, 28 Jul 1999 17:17:01 -0700
Subject: Re: Difference Tones
At 12:29 PM 7/28/99 -0700, you wrote:
David Fairweather

The best recorded example of the use of difference tones that I've ever heard was on the live version of "Hush Hush" recorded by the Siegel-Schwall band back in the 70's. (Not to be confused with the much inferior version on their more recent "ReUnion" CD). To my knowledge, the original is not available on CD. Too bad, Corky Siegel's solo is truly amazing...

What amp are you using? The choice of mike seems to make a big "difference" too - I get better difference tones through my green bullet than using anything else I've played.

-Li'l Geo
>

Good news to all. The latest edition of ICE, a magazine about collecting music and CDs indicates that several of the old Siegel Schwall recordingsare to be released on CD. The label was obscure. I don't know anything about sources. But replacing the vinyl is on my priority list.Ask your CD vendor.

From: John Thaden jjthaden@flash.net Date: Wed, 28 Jul 1999 02:19:42 -0500
Subject: Re: Difference Tones

Yes, the pitch of the difference tone is affected, since a difference tone is exactly that--the difference in frequency between the two tones producing it. Suppose you suck on holes 7 and 8 of a Bb diatonic harmonica. These notes are A and C, respectively, and the interval is a minor third. Suppose also that the A on the 7-Draw is tuned exactly to 880 hertz.

Now consider two cases: where the Bb harp has just intonation (JI), or equal intonation.

Try this same analysis with other pairs of notes and you'll quickly see that this example is actually a rather benign one. With some other pairs of notes, equal temperament results in difference tones that are extremely dissonant and unpleasant.

Some control of difference tones is possible by slightly bending the pitch of one of the two notes being played. David Therault (Magic Dave, BluesGeek) and others have addressed this quite nicely within the last 18 months on Harp-L, so the archives should yield a wealth of material.

Here's a post I found in the archives.
Brassha'per

In a message dated 4/13/98 5:58:48 PM, patm@globalnet.co.uk wrote:
>Christer wrote:

Please help! When I bend the draw chord in holes 3 and 4 I sometimes get an ugly extra sound. It mostly happens when I play one of the higher keys, D and upwards. F is the worst offender.
>
This sounds like a difference tone. It's due to some basic acoustics, the pitch of the difference tone being equal to the difference between the two frequencies which generate it. For example, if you played a pitches of 10kHz and 6kHz, you would get a difference tone of 4kHz. Free reed instruments produce very strong difference tones, in the upper range of higher keyed harps, they can be as loud oas the "normal" notes. Is it possible to get rid of that noise by tuning or must I learn to live with it?

You can't eliminate the difference tone, although certain playing
techniques can increase or decrease the volume if the tone. If the harp was
tuned in perefect just intonation, the difference tones would be perfectly
"in tune" with the notes that generate them (unlike on a tempered tuning,
where the difference tones are mostly inharmonic), but as you alter the
frequencies of the natrual notes during bending, the pitch of the
difference tone will also change. This can produce an interesting sound,
but it can also be quite distracting.

Ah, the wonders of 3-hole draw.

Pat is hinting at the possibility of controlling the nature of these
difference tones through playing technique. In a discussionI had with Pierre Beauregard, I remarked on how well Annie Raines was able to control the 3/4 diff tones. He said, "That's what she gets paid to do." How true. This is a very essential foundation for any blues player.

There is so much variety of expression to be had in the relationship of those two sets of reeds involved in playing 3/4 draw, and this is the first time I've attempted to describe it all as I experience it. So, it feels that I'm about to float into a veritable sargasso of confusion. I'm sure this information has been presented, more clearly, here or elsewhere, and this isn't likely the response that Christer is anticipating, but here goes.

As a general point, I think one of the ways of getting some control of these difference tones is by playing mostly hole 3 with just a crack of hole 4. The difference tone is reduced considerably. This is especially helpful where the harp isn't in JI, and where the difference tones can be pretty ratty. You can still get some dirt in the tone, but the focus on 3 draw can make the diff tones more agreeable to the ear.

Also, if the harp is set up in JI, or close, the two notes may have a tendency to work together a little easier across the full range of the bends, than if they are tuned to equal temperament. However, it is possible to compensate for the reeds being tuned to ET, by adjusting in the mouth. Various types of diff tones are created, in part, depending on whether the player makes adjustments using throat bending or mouth bending (or a combination thereof), and in part, depending on the mix of the two notes.

In JI, the 3rd (hole 3 draw on the draw plate) is a little flat of an equal 3rd, and the JI 5th (hole 4 draw) is a little sharp of an equal 5th. (Correct so far, Pat? Please step in and give us the benefit of your mind, if I give any false accounting, here. Also, readers are referred to download Pat Missin's "Altered States" for a solid priming on the subject of intonation, at http://www.users.globalnet.co.uk/~patm/ .)

The player can get a pleasing diff tone of the tonic (in 2nd position) by slightly pulling down hole 3 draw (the 3rd), using a throat bend (constricting at the k spot), while allowing a bit of 4D (the 5th) to bleed in. The ET 3D will actually have to be pulled down quite a bit, to work a pure harmony with the ET 4D, which is flat to JI.

The player may find that the place where the JI harmony kicks in is a very flat M3. This note and chord is fairly interchangeable in practice, as either a M3 or a m3. (This diff tone, and the natural unbent diff tone of a 3/4 in JI, are probably the 3/4 diff tones most central and essential to blues harp.) Usually, a controlled performance of a 3/4 draw chord bent even further down (in the throat) to a true b3 note (considerably more of a bend than the that which I first described), will produce a diff tone of the b3, which isn't necessarily undesirable, and is really useful on a IV chord or a tonic minor in 2nd position (or as a bIV chord or IVm in 3rd position, a #IVdim in 5th position, and so on...).

If the same type of adjustment is made to bring a pure harmony to the M3, using a mouth bend (vowel-like manipulation of the tongue), the diff tone will probably be a "sharp" M7. This isn't as "on" as the tonic diff tone created using the throat bend, but it works, because it's so sharp that it's close to the tonic pitch, and allows the player to get some of that nice round "wa" sound that comes with a mouth bend.

The important thing with all of these avenues is to find the places where the two notes come together in pure harmony. Otherwise, the complaint that started the thread will continue. To get the help from the harp in this, it's probably best to have your harp in JI, and to really get that Big Walter 3/4 diff tone on the unbent 3/4, you just about have to set your harp up in JI.

Another expression I've heard is achieved by banging pretty hard on the 3/4 with a lot of emphasis on the 4.

Thus far, we have covered achieving agreeable diff tones on the 3D and 3Db, and that is probably where most of the traditional styling is done. Any kind readers who are only interested in that very customary use can disregard the remainder of this post.

Now, digging deeper to the diff tones that come with the deeper bends. Bending the 3/4 to the 3Dbb, creates two pleasing diff tone potentials. When done with a throat bend, the 4D has a tendency to stay at its pitch, and a diff tone of the 5th (in 2nd position) results. This is especially useful in playing a V chord in 2nd position or for the tonic chord in 3rd position. The same 3/4 bend using a mouth bend, encourages the 4D to drop close to a 4Db, and can produce a diff tone reinforcing the 3Dbb pitch as chord root (with the 4Db as the M3rd). Very useful for the tonic chord in 4th position or a V chord in 3rd position.

Playing a the 3/4 with a 3Dbbb, using a throat bend, makes a diff tone reinforcing the pitch in 2B, making it especially useful as a tonic for 5th position.

I might suggest that these explorations may be most clearly experienced on G, A and C harps, at first. Back to Pat, I think that the mathematics explaning this, are all available in his Altered States. As we can see, there are enormous harmonic possibilities just in the draw/bend combinations of these two notes, alone. There are many others to explore in the other adjacent chamber associations of the instrument, and by adding tongue blocking, the opportunity to harmonize non-adjacent chambers presents quite an array of chordal and counterpoint potentials. And, course, that's just considering the possibilities for a richter-tuned, unvalved, "in- Discrete," "un-overblown," diatonic. Maybe that's why they call it a harmonica. (Ok, Dave, hit Send.) - -Dave Therault
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Which harps (particularly Hohner and LO) are which?

LO and GM are ET. Herings are JI. MS series and the Hohner handmades other
than GM are compromise tunings between ET and JI, but not either. All of these harps are unlikely to achieve their specified tuning, since factory tunings are notoriously crappy.

Which tuning is related to the tuning of a piano?

ET

What tuning is being used when a guitarist tunes to a tuner vs fret tuning? If he tunes each string to the tuner, then ET. If he tunes one string with the tuner and the other strings to that string by fretting or playing harmonics, then he is likely to arrive at something closer to JI, although most guitarists finish off by playing the main chords and making small adjustments so they all sound reasonably OK, in which case, the tuning is moved closer to ET. > >What I'm trying to find out is if there are certain types of harps I should >be using on certain songs.

Go to Pat Missin's website and get his file.

My ear seems to be getting better and once in a >while I play a note that doesn't seem to fit quite right and I know I'm in >the right mode and am in tune and the band is in tune . . . I first >noticed this playing cross harp with a country band which I think has >something to do with the flatted 7th (not sure, way over my head here). I >noticed a big difference when I used a country tuned harp.

Yes, the flatted, or blues 7th in cross harp isn't going to work for some country songs, whose melodies include the regular 7th, so cross-harp on a Richter harp was not the right mode for those tunes. But this has nothing to do with JI vs. ET. >
>My rational default has been "if the old boys could do it then the Marine
>Band should do the job (or S20)" I know for example that Lee Oskars are
>tuned a bit sharp which makes them sound a bit brighter (at least I think I
>know this) but they are still tuned JI (I think).

No, ET, so the chords may sound rougher and less pleasant to you than on a Hering.

To me, the most noticeable thing about a JI harp (besides the really pleasant chords) is that the 5D note is going to sound flat to you when playing some melodies. ET harps are really needed by people who use lots of different positions--in 12th (first flat) position, for instance, that rather flat 5D note is the tonic, and it's going to sound pretty horrible on a JI harp. If you mostly play crossharp and play lots of chords, especially if you play through a close mic like a GB, then the JI harps or the Hohner compromises may sound lots better to you.
 
John Thaden
Little Rock, Arkansas, USA