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#1125306 04/04/04 04:17 PM
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Ariel Offline OP
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This is a much belated expression of thanks to all the expert posters who replied in October to my thread question "What is 'Attack'?"

After bcarey, and Steve and KlavierBauer weighed in I became so overwhelmed with the hyper-expertise and detail expressed by ryan, pete blues and BDB that I didn't know how to reply at all - even to ask intelligent questions.

I had therefore planned to write a witty rejoinder expressing both my gratitude and my confusion, incorporating some of the terminology - especially from ryan's linked article - see below...Only I couldn't put that together either.

Ryan, you and BDB (BDB, oh thou math major, you REALLY pushed me over the edge)- you obviously know so much it's become impossible for mere mortals to approach your celestial heights! laugh

...But, anyhow, it's been hanging over me that you all put a lot of effort into your answers and I never even expressed my appreciation. And I really DID appreciate them, although I'm not positive I have a real grasp of the concept of "attack" - at least not in sine waves. wink

When sustain turns into decay, is a subject of some confusion too, but I guess it's somewhere between licking the sound envelope and ripping it open impatiently... cool

You guys have impressive expertise. BDB and pete...I liked your jokes at the end!

Ariel
***********************************************

[Linked Image]

The typical decay of a piano tone is shown in Fig. 1, which displays the sound pressure level as a function of time. We see that the string is struck by the hammer at about t = 2 seconds, and the damper is released, stopping the vibration, at about t = 17 seconds. The vertical scale is in decibels, so that the ordinate of the graph is proportional to the logarithm of the pressure amplitude. In such a plot, the drop in level would appear as a straight line if the decay of the sound were of a type called exponential, which is what a physicist would expect from a linear system such as the string and the soundboard. Instead, it is clear that the curve breaks into two portions of quite different decay rates. The initial portion, called "prompt sound," drops (in this case) at a rate of about 8 dB/sec; the final one, called "aftersound," at less than one-quarter that rate. As we shall see, the prompt sound is simply related to the theoretical decay rate determined by the string's coupling to the soundboard; whereas the aftersound, which gives the piano its perceived sustaining power, represents the "miracle."

emphasis mine!
*******************************************
pete:
Quote
an analog square wave created by a transistor gate actually doesn't have any attack time or overshoot, since as soon as the gate opens, electricity is flowing. The overshoot happens in the digital world, when trying to simulate a square wave with a sum of sine waves, in order to avoid aliasing.
And as for you, pete - you cut that out!


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#1125307 04/04/04 06:28 PM
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Ariel,

What is Attack?

"TomK."

Need you ask more? wink

#1125308 04/04/04 07:11 PM
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She could ask you to sit on one. laugh

#1125309 04/05/04 03:27 AM
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With respect to all of the learned opinions and observations that have gone before — Unless I've missed something (As I might well have done. I’ve just returned from a trip and it’s late.) there is at least one point that seems to have been missed.

When a piano hammer strikes a string (or string set) it causes a creates an abrupt and violent physical displacement in the taut wire(s). This displacement will ultimately stabilize into some more-or-less coherent wave motion, or oscillation, as it develops into the characteristic wave motion that ultimately drives the bridge and creates the relatively steady-state sound of the piano. “Relatively” because it is not really steady-state, the piano strings are very lossy oscillators and the vibrating energy is decaying at some usually variable rate. Still, it is sustaining enough for us to identify pitch and volume.

However, before the string settles into this more-or-less coherent oscillating motion there is a brief period of utter chaos. There is a broadband wavefront that radiates out away from the hammer impact point and only becomes a coherent wave motion over some finite period of time — a few milliseconds down toward the bass, less up toward the treble (this time period is not clearly defined and depends on many variables such as the length of the scale, its tension, etc.). This chaotic wave motion reaches the front string termination well before it reaches the bridge (there is less distance to cover) and well before it becomes anywhere close to coherent. On reaching the front string termination, be it an agraffe or a V-bar, it causes the plate to vibrate.

Now, the plate may not actually be a very efficient soundboard, but it does move enough to create at least some sound energy. Some of this motion, along with some residual energy that is coupled to the rim and other case parts, creates most of the sound we call “hammer knock” when it gets too loud but which is otherwise so closely linked to the tone production of the piano that when it is missing (i.e., deliberately removed by careful editing) our ears often fail to recognize the resultant sound as coming from a piano.

Going the other way, this chaotic wavefront also travels toward the bridge(s). Along the way it is transforming itself into a coherent waveform, but this transformation may not fully occur until well after the initial wavefront reaches the bridge. So, although the string’s energy is very rapidly settling down into the aforementioned more-or-less steady-state wave motion, there can also be a brief period of relatively broadband noise generated by the soundboard. Again, how long all this takes is a function of scale length and tension.

All of which brings me to my answer to the original question: that period of time during which the motion of the string(s) is primarily chaotic, both at the front string termination and at the bridge (where it is coupled to the soundboard assembly), and the sound generated during this period of time, is what I call the “attack” period of the piano waveform envelope.

ddf


Delwin D Fandrich
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I totally agree with Del, (and appreciate his precise description !)

To me attack is percussion noise, mostly, that stabilize more or less fast in tone.

thats the most important part of the tone to be tuned, as the way the attack provide energy to the tone is how the tone will be projecting.

That is also the sensation that the pianist feel under its finger (he does not feel the sustain or dwell)
So you can have a piano perfectly tuned but with something missing too the pianist : the attack which have not be treated.
thats normal because the ear of the tuner close when predicting the noise.

Last edited by Kamin; 12/13/09 02:50 PM.

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Olek #1333052 12/24/09 02:25 PM
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What's the difference between sustain and decay? Are they both sections of the graph were the volume of tone is decreasing....?

I just reread the explanation in the most recent edition of the Piano Book(4+ years ago, around p. 41). Fine put them in this order: attack, decay, sustain. He defines decay as the initial and quick drop off from the peak of the attack portion of the graph and sustain as the longer part of the graph where the volume more slowly dies to zero.

1. Are the terms decay and sustain usually used as per the Fine explanation or is there disagreement on how they're used? There seems to be a difference of opinion about the order/meaning of decay and sustain compared to earlier posts.

2. In good my view good sustain involves two things:
(a)maybe most importantly, the portion of the graph where the tone drops at a slower rate starts a volume that's not too low compared to the maximum attack volume. In other words, if a tone remains audible for a long time but only at a very low volume compared to the attack maximum, that's not useful or good sustain.

(b)How long it takes before a tone dies out to the useless(not meaning inaudible)stage.

Is this a reasonable explanation of good sustain?

(If I had a graph it would make things easier to ask/explain)

Last edited by pianoloverus; 12/24/09 02:50 PM.
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