Internal delay of VPC1

kawafanboi

Presumably, triggering the 3rd sensor is equivalent to touching a string with a hammer. It seems so.

On an acoustic piano the blow distance (distance of hammer at rest to string) is usually 47mm. The hammer is detached at escapement which is 1mm before the string. The key has a total travel of 10mm, however the escapement is also 1mm before bottom. However the ratio of hammer travel to key travel is 46 / 9 ≈ 5. That means that for the last 1mm of key travel the hammer should travel 5mm. But it travels only 1mm to the string. Hence, the hammer hits the string before the key bottoms out. I’m not sure where they put the lowest sensor on a digital piano but I’m sure it’s near the bottom. I doubt a digital piano will thus generate a strike event sooner than an acoustic piano. I’m not even sure that’s something good either. But there’s also scanning logic delay. And sound buffering delay.

In an acoustic instrument, the moment of impact of the hammer can be either before the key reaches the bottom, or after. It depends on the style of the game. For a numeric keypad, this time between the hammer stroke and the bottom of the key is most often the same.

BTW, that last millimeter of key travel after escapement is called aftertouch and is variable, depends on pianist preference, apparently the fine timing advance between hammer hitting the string and key bottoming out is important and affects touch perception. DP manufacturers don’t talk about that because apparently the scanning speed introduces some rather unpredictable delay that might be higher than the fine aftertouch setting on an acoustic piano.

This millimeter is extremely important. If the distance is large, you will not be able to play expressively quietly. Or it will be very hard. If it is too close, you will get a hammering on the string. In this setting, it is very important to keep this setting the same across the entire range of the keyboard. If there is an unevenness, then some notes will seem deaf, and others will suddenly scream. It is very inconvenient to play then.

SouthPark then do they encounter latency issues to any extent that that makes the user feel that there is something wrong with the note timing

It is precisely because the delay values within the VPC are different that it can cause some inconvenience during play. If this delay were constant and the same, it might be nicer.

These inconveniences may manifest themselves when you play an acoustic instrument after playing on VPC. Or, when you start playing more, such as Liszt's pieces. If you play music on a VPC in a relaxed manner, then you are more likely to experience few or no inconveniences.

David B

Everything is right. It seems that it is preferable to connect the keyboard via usb to the computer and the sound card via usb to the computer.

scherbakov.​al It is precisely because the delay values within the VPC are different that it can cause some inconvenience during play. If this delay were constant and the same, it might be nicer.

A very interesting topic! It will be also interesting to later see if only the vpc1 has this relatively large variation in time between input to the usb system and output of the usb system. The tests on other controllers would probably require the same hardware/software setup, and the same testing. Such as how many notes are triggered, and how they are triggered etc.

And also to make sure that all the notes data going to the input to the usb system all appear at the input with the approximately the same start time.

scherbakov.​al Everything is right. It seems that it is preferable to connect the keyboard via usb to the computer and the sound card via usb to the computer.

I did away with the midi-DIN cables and it cleaned things up back there.

Now it's USB midi direct to computer and Babyface Pro via USB to computer. In my VST settings it's Numa X Piano for midi input and Babyface for output. I don't really notice a difference in latency, but I like things cleaned up.

God Bless,
David

Some latency details discussed here : LINK

To the question about MIDI-DIN:

(Channels 0 and 1 are usb, channel 2 is din, 3 is the third sensor.)

A midi message over USB is sent after it is sent over DIN. Almost immediately.

The question arose, does the amount of delay depend on velocity? For example, the Kawai MP11 creates a different amount of delay depending on the speed. This is done for some approximation to the actions of acoustic instruments. Maybe the VPC1 is doing something similar too. Or maybe he just has a tremor inside. Judging by the three measured notes, it seemed that the jitter when the DIN output was turned on inside seemed to be less. Or it was just my imagination.

scherbakov.​al The question arose, does the amount of delay depend on velocity?

It may well depend on an estimated velocity. When the the tracking system doesn't know exactly where the key is and what it is doing … eg. gone stationary, or still moving slowly, which direction it is going, speed, acceleration etc, then it can become a situation of determining the issues/challenges, and sorting it out. That's the challenge and fun that the developers have.

For the third sensor … if the key is coming back up, and a release velocity was measured by the other sensors … then what happens if the key does something different on the way up after the volocity estimate was made. It may turn into a challenge of what other measurement and tracking/monitoring techniques we need, that need to be used - without impacting negatively whole system performance.

Very interesting discussion.

I have an acoustic piano retrofitted with an optical sensor rail under the keys.

So it behaves a bit like a continuous multi-sensors system because I can set the key depth where I want the note-on to be generated and also the key depth to trigger the note-off.

But once set, I think the note-on midi event is always generated for a fixed depth.

What is interesting is that I can play both the acoustic sound and the VST sound at the same time to listen to timing discrepancies.

First, this system allows to set a shallow key depth for note-on so that the acoustic and VI sounds are reaching my ear at the same time.

But the by reducing the note-on key depth, you also reduce the precision of how velocity is measured. So there is a trade-off to find here between low latency and accuracy.

Then something that is rarely discussed : the VI sound becomes delayed compared to its acoustic counterpart as I reduce the velocity.

So let’s say both sounds arise at the same time when playing mf, then acoustic sound will arise sooner when playing pp. Maybe this is due to bending occurring in action parts that delay the hammer when playing louder…

Well, I wonder if keyboard manufacturers have ever addressed this phenomenon in their products (or maybe they are not even aware of it 😅). But there is plenty of room for improvement here, between jitter and real action behavior…

They are highly likely aware of it. But probably leaving it as secondary. Evolution of digi-mech is still going on. The results are very impressive these days. In the hands of us … a digital piano produces amazing music and expression to trigger very deep emotion and/or musical joy/satisfaction, regardless of timing variance etc. And digi-mech is still evolving.

In case some are moreinterested, this is the chapter of the Askenfelt & Jansson study dealing with that particular point :

https://www.speech.kth.se/music/5_lectures/askenflt/keybott.html

Paulo164 https://www.speech.kth.se/music/5_lectures/askenflt/keybott.html

A close-up of the events at string contact at three dynamic levels shows two interesting facts (see Fig. 4). One observation is of special interest for the pianist. It turns out that at a certain dynamic level, about mezzo forte, the key reaches its bottom position at the same moment as the hammer strikes the string, while at other dynamic levels this synchrony is dissolved. For those of us who don't play the instrument, this observation may not seem very interesting, but every piano player can tell that the bottom feeling of the key is an important feedback from instrument.

Does that suggest inconsistency in behaviour? That probably means loss of control, or more room for loss of control due to the timing reference shifting around - depending on position rate of change, and where the key push begins (in position).

SouthPark

I don’t think so.

That’s a key > hammer > string transfer function, perfectly predictable for the pianist, once accustomed.

It’s similar as most of sports including a device (tennis, golf,…). The stronger you strike, the more the body is in advance of the device hitting the ball.

Paulo164 It’s similar as most of sports including a device (tennis, golf,…). The stronger you strike, the more the body is in advance of the device hitting the ball.

For golf, the ball stays in one spot. So it won't be like golf. For tennis, the ball is coming at a certain speed etc, so it will be more like tennis - maybe. What they probably need to do is to gather a consortium of formal testing groups - universities etc, and set up some sort of standard timing studies, to see if they can measure the timing accuracy from a bunch of different pianists. The results will be handy, or at least interesting. Getting proper testing and documenting done could be challenging. But interesting.

I feel like I'm having a deja vu (or is deja entendu) with this conversation. Wasn't this already discussed at length, also in the context of acoustic pianos where the hammer speed greatly differs between ppp and fff, and hence the time difference between key bottoming and sound being produced -- even ignoring the time it takes to reach your ears -- also greatly differ? IIRC such time can vary from noticeably before the key bottoms (for fff) to well after (for ppp)? I think this becomes such an obvious observation when you entertain the extreme case of "infinitely after" in the case of "too soft of a keystrike for the hammer to ever reach the string"....

True. But even if they do get ppp or pppppp etc -- they better make a piano that doesn't have the pedal noises and internal mechanism noises. Kadunk, clunk, thump, fwip, shhhh etc. Otherwise, it just 'undoes' all of that ppppppp etc.

All these hammer and pedal noises are indeed unnecessary. The truth is, digital/software piano manufacturers put them because it’s cheap and easy and is a poor attempt at covering up the really important features that are missing in their emulations.