Double Bass Sound wave analysis: There's your problem, right there

[Dr. Jake]

I often find myself in a situation I'm sure is familiar on this side of the forum: trying to explain to another musician (usually a drummer, guitarist, or saxophonist) that an acoustic bass, amplified with a pickup, loses its unique sound and rhythmic feel. The more I've experimented with pickups and amps, the more I've felt that the acoustic bass (played pizzicato) possesses a particular attack and decay that contributes something vital to the swing feel of jazz.

Recently, a feedback nightmare gig using a mic (SM57 through the afterlengths) and a very disappointing experiment with a Gage Soundclip sent me back to the pickup/mic marketplace one more time. I came upon this set of clips: Invalid Link Removed

I was particularly struck by the graphical representation of the sound waves. They seem to show what I've been ranting at my bandmates about for years: the attack and decay become 'sharper' through a pickup. Is it that the pickup is responding late - missing the first part of the note?

I'd be interested to know how those with more knowledge of acoustics and/or electronics than I have would interpret this - and perhaps speculation about ways in which we might be able to push pickup development toward a cure for this problem?

 

[drurb]

Well, timing is everything! Take a look here, Dr. Jake.

You'll see that, days ago, I posted comments quite consistent with your sentiments. The attack/decay profile of the acoustic output of the DB are what give it the characteristics most of us love and which define it. That's actually true for any musical instrument.

Actually, I've found the effects of typical pickups to be the opposite of what you described. That is, typical pickups yield an, overall, less pronounced temporal attack/decay profile that removes the perceived percussive "thump." The waveforms at the link reveal that quite clearly. At that link, you can both hear and see how the Ehrlund transduces a rather natural (using the mic'ed bass as a reference) attack/decay profile that is more pronounced ("sharper") than that transduced by other pickups. Thanks for posting it.

 

[Dr. Jake]

I was searching for the right word to describe what I was seeing in the wave forms and "sharper" probably wasn't the best choice.

Looking back and forth between (for example) the waves produced by the mic and the Realist, the latter's attack looks stronger and less complex.

 

[drurb]

It's important to look at the temporal envelope formed by the attack and decay profiles. These square with what I hear and what I surmised by listening. The pickups tend to have a reasonably quick rise but not the pronounced decay that is evident with the microphone. What the wood top does is different from what's going on, say, at the bridge wing or bridge foot. A microphone picks up the characteristics of what the wood is doing. Interestingly, so, apparently, does the Ehrlund and that seems to explain why like it as much as I do.

Now, consider what happens when you don't have a pronounced decay. The average power is fairly constant across a substantial duration. You adjust the amp for the level you want and off you go. Suppose you now switch to a mic or pickup that transduces the attack/decay profile more characteristic of the DB played acoustically. The same average level will now be characterized by a very high, relatively short-lived, initial level and a longer trailing portion at a substantially lower level. The result? Percussive attack followed by a more modest sustained level. In other words, more like what we hear when the instrument isn't amplified at all.

It all seems to fit together. I'm really glad you posted that link! I may download those waveforms and do some analyses on them.

 

[William Hoffman]

That is insightful and interesting. A mic is located "off wood" (so to speak) and transits vibration picked up in the air, while your typical pickup, say a Realist, transmits vibration from directly on the top of the instrument. The Ehrlund is both. Just trying to understand you drurb, is that consistent with what you are trying to say?

 

[iiipopes]

I have my Full Circle "upside down," and it has a rounder attack, just as much sustain, but more "thump" in its sound profile, which I can tame or not as desired for the particular gig at will with my fdeck.

Fun reads to the links posted. Thanks. I haven't thought about "ADSR" (Attack Decay Sustain Release) or waveform analysis (sine, square, triangle, sawtooth) since early synthesizer days!

 

[drurb]

That is insightful and interesting. A mic is located "off wood" (so to speak) and transits vibration picked up in the air, while your typical pickup, say a Realist, transmits vibration from directly on the top of the instrument. The Ehrlund is both. Just trying to understand you drurb, is that consistent with what you are trying to say?

Yes, indeed. To expand a bit, a mic really is picking up virtually only the response of the wooden, resonating box we call the the double bass. The vibration of the strings through the bridge, into the bass bar, sound-post, and on and on really form a complex mechanical filter, or set of filters, that change(s) the nature of the vibration dramatically. The acoustic output is, of course, the sound of the instrument.

While the Realist transduces the sound that is influenced directly by one small area of the top plate (and indirectly by much more), as I see it, that vibration is not characteristic of the properties of the whole vibrating box. After all, the Realist is sitting right over the bass bar so what excites it is largely direct transmission from the bridge foot.

The Ehrlund is a different animal. Even if it picked up no airborne vibration, it is sitting on a resonant part of the top-- a part that is part of, or has undergone, much of the mechanical filtering. Moving it to different places on the top, allows one to choose just which parts of the vibration (think Chladni patterns). I did some tests with the Ehrlund and, so far as I can tell, it is quite insensitive to airborne vibration. The vast majority of what seems to drive it is directly transmitted mechanical vibration.

I'm not trying to suggest that a pickup like the Realist or Rev Solo, or Full Circle is bad. In fact, it's amazing to me that they sound as good as they do! IMO, the principle of the Ehrlund is better. To me, it sounds better and there seems to be good reason why. Of course, if the Ehrlund had a lousy transducer inside, the better "principle" would be meaningless. The Ehrlund is more susceptible to feedback and the placement requires more patience than other types of pickups but, so far, I've been rewarded for my efforts.

 

[martinc]

Interesting analysis of the sound that pickups and mic's reproduce.
When I closed my eyes and forgot about the technology involved and went with my gut feel about which sound I thought sound most like a double bass....I'd have to give the nod to the Realist.
I surprised myself. The Realist is not a pickup I have ever used or even considered much.
I'd be interested in how others reacted to the sound samples.

 

[William Hoffman]

Yes, indeed. To expand a bit, a mic really is picking up virtually only the response of the wooden, resonating box we call the the double bass. The vibration of the strings through the bridge, into the bass bar, sound-post, and on and on really form a complex mechanical filter, or set of filters, that change(s) the nature of the vibration dramatically. The acoustic output is, of course, the sound of the instrument.

While the Realist transduces the sound that is influenced directly by one small area of the top plate (and indirectly by much more), as I see it, that vibration is not characteristic of the properties of the whole vibrating box. After all, the Realist is sitting right over the bass bar so what excites it is largely direct transmission from the bridge foot.

The Ehrlund is a different animal. Even if it picked up no airborne vibration, it is sitting on a resonant part of the top-- a part that is part of, or has undergone, much of the mechanical filtering. Moving it to different places on the top, allows one to choose just which parts of the vibration (think Chladni patterns). I did some tests with the Ehrlund and, so far as I can tell, it is quite insensitive to airborne vibration. The vast majority of what seems to drive it is directly transmitted mechanical vibration.

I'm not trying to suggest that a pickup like the Realist or Rev Solo, or Full Circle is bad. In fact, it's amazing to me that they sound as good as they do! IMO, the principle of the Ehrlund is better. To me, it sounds better and there seems to be good reason why. Of course, if the Ehrlund had a lousy transducer inside, the better "principle" would be meaningless. The Ehrlund is more susceptible to feedback and the placement requires more patience than other types of pickups but, so far, I've been rewarded for my efforts.

Interesting that the EAP is insensitive to airborne vibration. Goran's website now states that it simply picks up vibration from the spot where it is on the top. He once suggested to me that airborne vibration did play a role, but it stands to reason that your test result is correct. The EAP does not respond to airborne vibration when it is not attached to an instrument. But what it has going for it is its "mobility" that is, its ability to be placed in those spots on the instrument that give better acces to the kind of vibrations that sound best amplified.

Why do you think the EAP has a more mic-like attack / decay pattern as you suggested in the earlier postings?

 

[drurb]

Why do you think the EAP has a more mic-like attack / decay pattern as you suggested in the earlier postings?

I think it is because it's transducing what the resonant portion of the top plate is actually doing at the location it sits. This will not be exactly the same as the response of the bass as a whole as picked up by a microphone but it is apparently closer to that than what a typical pickup does. It makes sense that the resonant portion of the top is responding, in terms of attack and decay, in a manner that's very different from right under the bridge foot.

With the Ehrlund, you can fish around for the spot you find most desirable in that sense. As you said,

But what it has going for it is its "mobility" that is, its ability to be placed in those spots on the instrument that give better acces to the kind of vibrations that sound best amplified.

Oh, just a bit more on the airborne vibration. I brought the Ehrlund into the lab and connected to an oscilloscope. I then placed it right over the center of the grill of a monitor speaker. Even with a rather intense signal, the Ehrlund was virtually unresponsive. Rub your finger over it though, and the output takes right off.

 

[William Hoffman]

Gotta hand it to you drurb. I hear you. Listening to Jonas' sound clips via the link in the OP, the EAP really jumps out at you as the most mic-like or even unplugged sounding pickup. That is, it transmits the front end pop of the note best from among Jonas' selection of pickups, then settles down for the rest of the note with a marked decay before the thump of the next note. That, plus its natural acoustic sound overall with finger and string articulations, make it stand out in this regard. The other pickups compared do not transmit this dynamic aspect to the same degree.

These pickups are all amplifying the same bass and strings and setup. The attack and decay on all of them, acoustically, are in reality essentially the same and the only difference is the way the pickups transmit basically the same vibration. The Realist "wood" (under the bridge foot) sounds better than I thought it would, more finger articulations and less grain than I expected from having played an earlier make of Realist for years. The Bassbalsereit (embedded in the bridge leg) sounds smooth and flat and has much less contrast between thump and decay than some of the others, but with huge deep sustain, and kind of reminds me of NHOP's style of playing. These are all good sounding, acceptable pickups, it's just a matter of how you want to be heard.

Now the EAP is of course not a mic, but it just has the right properties and location to transmit what comes out of the amp sounding very similar to the bass played acoustically or with a mic. I am tempted to say the attack and decay are with the EAP even more pronounced than on the clip made with the DPA 4099.

 

[drurb]

Gotta hand it to you drurb. I hear you. Listening to Jonas' sound clips...

Thanks! This all motivates me even more to grab the waveforms at the link and analyze those attack/decay profiles and post some pics. Stay tuned, but it may take a while for me to get to it.