Velocity and Pressure are inversely proportional to the Area of cross section of the body through which a fluid is flowing. consider figure 1: An ideal fluid(that. through a barrier without the use of any mechanical connection. Because these drive couplings .. pressure affects both slip in the pump and motor speed — both of which affect the flow rate. .. Hydraulic Fluid, synth. A. A. A. A. N. A. N. A. A. D. The value grid controls extra MIDI data, such as velocity, program changes, notes equally by the percent given in relation to the original velocity, while an One such example is Qsynth, written by the same programmer as QJackCtl and Qtractor. Sound waves, being oscillations of pressure, are measured by the cyclic.
High-speed FireWire connections are also available on older computers without a high-speed USB connection. FireWire devices are sometimes incompatible with the standard Fedora Linux kernel.
External USB Connection Sound cards connected by USB are becoming more popular, especially because notebook and netbook computer are becoming more popular. The quality can be as good as an internally-connected sound card, but the USB connection may add additional latency. USB-connected sound cards are generally the most affordable sound card for amateur musicians who want a high-quality sound card. Choosing a Connection Type The connection type is only one of the considerations when choosing a sound card.
If you have a desktop computer, and you will not be using a notebook or netbook computer for audio, you should consider an internal PCI or PCI-Express connection.
If you want an external sound card, you should consider a FireWire connection. The connection type is not the most important consideration when choosing a sound card. The subjective quality of the analog-to-digital and digital-to-analog convertors is the most important consideration. Sample, Sample Rate, Sample Format, and Bit Rate The primary function of audio interfaces is to convert signals between analog and digital formats. As mentioned earlier, real sound has an infinite possibility of pitches, volumes, and durations.
Computers cannot process infinite information, so the audio signal must be converted before they can use it. A smooth, continuous waveform approximated by discrete steps.
The red wave shape represents a sound wave that could be produced by a singer or an acoustic instrument. The gradual change of the red wave cannot be processed by a computer, which must use an approximation, represented by the gray, shaded area of the diagram.
This diagram is an exaggerated example, and it does not represent a real recording. The conversion between analog and digital signals distinguishes low-quality and high-quality audio interfaces.
The sample rate and sample format control the amount of audio information that is stored by the computer. The greater the amount of information stored, the better the audio interface can approximate the original signal from the microphone.
The possible sample rates and sample formats only partially determine the quality of the sound captured or produced by an audio interface. Sample A sample is a unit of audio data. Computers store video data as a series of still images each called a "frame"and displays them one after the other, changing at a pre-determined rate called the "frame rate".
Computers store audio data as a series of still sound images each called a "sample"and plays them one after the other, changing at a pre-determined rated called the "sample rate". The frame format and frame rate used to store video data do not vary much. The sample format and sample rate used to store audio data vary widely. Sample Format The sample format is the number of bits used to describe each sample.
The greater the number of bits, the more data will be stored in each sample. Sample Rate The sample rate is the number of samples played in each second. Sample rates are measured in "Hertz" abbreviated "Hz"which means "per second," or in "kilohertz" abbreviated "kHz"which means "per second, times one thousand. Common sample rates are Bit Rate Bit rate is the number of bits in a time period. This measurement is generally used to refer to amount of information stored in a lossy, compressed audio format.
To calculate the bit rate, multiply the sample rate and the sample format. For example, the bit rate of an audio CD Conclusions Both sample rate and sample format have an impact on potential sound quality. The capabilities of your audio equipment and your intended use of the audio signal will determine the settings you should use. Here are some widely-used sample rates and sample formats. You can use these to help you decide which sample rate and sample format to use. Used for audio CDs. Bit rate of Audio CDs are recorded with these settings and "down-mixed" later.
Maximum settings for DVD Audio, but not widely compatible. Used for SuperAudio CDs. Sample rate and sample format are only part of what determines overall sound quality. Although these restrictions sound severe, the Bernoulli equation is very useful, partly because it is very simple to use and partly because it can give great insight into the balance between pressure, velocity and elevation.
How useful is Bernoulli's equation? How restrictive are the assumptions governing its use?
Bernoulli’s Effect – Relation between Pressure and Velocity - Nuclear Power
Here we give some examples. The flow therefore satisfies all the restrictions governing the use of Bernoulli's equation. Upstream and downstream of the contraction we make the one-dimensional assumption that the velocity is constant over the inlet and outlet areas and parallel. One-dimensional duct showing control volume.
When streamlines are parallel the pressure is constant across them, except for hydrostatic head differences if the pressure was higher in the middle of the duct, for example, we would expect the streamlines to diverge, and vice versa.
If we ignore gravity, then the pressures over the inlet and outlet areas are constant. Along a streamline on the centerline, the Bernoulli equation and the one-dimensional continuity equation give, respectively, These two observations provide an intuitive guide for analyzing fluid flows, even when the flow is not one-dimensional. For example, when fluid passes over a solid body, the streamlines get closer together, the flow velocity increases, and the pressure decreases.
Airfoils are designed so that the flow over the top surface is faster than over the bottom surface, and therefore the average pressure over the top surface is less than the average pressure over the bottom surface, and a resultant force due to this pressure difference is produced.
This is the source of lift on an airfoil. Lift is defined as the force acting on an airfoil due to its motion, in a direction normal to the direction of motion. Likewise, drag on an airfoil is defined as the force acting on an airfoil due to its motion, along the direction of motion. An easy demonstration of the lift produced by an airstream requires a piece of notebook paper and two books of about equal thickness. I then painted over the exposed copper with polyurethane.
I'm not sure if that's the optimal insulator to use, but it seems to work. One of the neat things about doing it this way is that the ends of the traces can be trimmed to the appropriate length and then jammed into a solderless breadboard.
No need to contrive some sort of connector. Somehow, I managed to do this whole project without soldering a single thing. I'm not sure if that's something to be proud of, but I am. The Keybed Base At around this point it became obvious that my original keybed wasn't big enough to fit the electronics I wanted to add, so I made a larger base. Once again, this was made of plywood.
I used a router to make a recess up top so that I wouldn't have random stuff sticking up quite so high. I used copper tape with conductive adhesive as a ground plane. I live next to a light rail line, so I tend to be a bit paranoid about shielding everything I can from cycle hum. I left room at the upper left for a Raspberry Pi and its various connectors. Pressure Sensors one hundred and fifty-six electrical contacts exposed So, how does this whole pressure sensor thing work, anyways?
Well, over the "circuit boards" with their electrical contacts that make up the bottom layer is a layer of a film that has the interesting property that applying pressure causes its electrical resistance to drop significantly.
This stuff comes in 11" squares, so unfortunately it's not possible to just use one big sheet. One sheet covers two octaves, so I had to use two and a half sheets. Originally, I used two layers but later changed my mind and reduced that to a single layer. It's worth noting that I purchased a huge roll of Velostat hoping it would perform the same as the stuff Adafruit sells, and I could use a single large sheet across the whole keybed and not have any seams.
Unfortunately, it doesn't seem to have the same electrical properties and I'm not sure if it's at all usable as a pressure sensor. Adafruit also sells this stuffwhich is more expensive than their other film and is only available in smaller squares, but it seems to be more responsive. Its resistance is also a lot higher, which in general is good because it means less current wasted, but the MCPs aren't designed for high-impedence outputs, so they might need a buffer.
I might give it a try if I build a version 2. On top of the pressure film goes a layer of plain ordinary aluminum foil, which is connected to ground. Analog to Digital Conversion of Key Pressure At the other end of our electrical circuit, the electrical contact under each key is connected by its long copper wire to a pull-up resistor connected to a voltage source and one input of an ADC chip basically, a digital voltmeter. These are commonly used to add analog inputs to Raspberry Pi projects and are supported by Wiring Piso you don't have to do much work to start using them.
Each MCP has eight inputs and reads ten-bit values 0 to MIDI volume is only 7 bits, so that gives us three extra bits of precision. We need 4 MCPs per octave, or 20 in total in order to construct what is basically a channel digital voltmeter. A single MCP is not quite four dollars, so twenty of them make up the most expensive part of the keyboard. SPI busses are fairly simple; they have a clock wire, a master-out-slave-in wire, a master-in-slave-out wire, and a slave select wire.
It's that slave select wire that's a problem. We can daisy-chain as many MCPs as we want on one big long bus, but in order to use any of the devices we need to ensure that only one is enabled at a time. If more than one is enabled, they'll both try to send data at once and we'll have data corruption. The most straightforward thing would be to run twenty wires from the RPi, one to the chip-enable pin on each MCP This could work, but it consumes a lot of pins.
The RPi does have a lot of pins to spare, but we might want to use them for something else. Better to find a more pin-efficient solution. This seemed like a great application of a shift register. A shift register has an input and a clock pin, and stores some bits which are sent to output pins.
When the clock ticks over, the shift register reads the input to determine the new value for its first bit, and shifts the rest of the bits over by one. Shift registers can be chained, so with three 8-bit shift registers, we can accomodate our 20 MCPs.
We just need to set the shift register to activate the first MCP, read its values, cycle the clock which will enable the next MCP, and so on. This all sounded simple and elegant. It also doesn't work, because of one of the MCP's strange little quirks. Apparently, in order to read all eight values from an MCP, it is necessary to read the first value, disable the chip, re-enable it, read the second value, disable it, re-enable it, read the third value, and so on until all the values are read.
Our simple shift register scheme doesn't provide us with a way to toggle the enable bit on and off without shifting. The solution I arrived at was to use some logical gates to combine the output of the shift register with the RPi's hardware slave select line.
So, we can toggle the slave select on and off to read successive values from a single MCP, then cycle the clock to select the next MCP and do it again. This takes a lot more chips than I wanted, but it doesn't use very many pins. So, I guess it's a success, even though the top of my keyboard now looks like a plate of spaghetti. I'm glad I used solderless breadboards; if this were a proper circuit board, I would have had to order multiple revisions. Raspbery Pi tangle of wires I used a Raspberry Pi 2 as my microcontroller.
I could have used a different microcontroller, but the RPi is inexpensive and seemed to be the best option for what I wanted to do. HDMI out wasn't necessary, but it's nice to have in case I come up with some cool visualization tools or I want to debug the system by using its desktop environment.
That's fine; I don't really need wireless networking for this project. In fact, it's probably better that I don't have it -- this isn't meant to be a high-security device, and I don't want it to become part of the so-called "Internet of Other People's Things". Better to use physical ethernet occasionally for debugging than have it permanently on the network. There were some things I had to tweak to get the RPi to work the way I needed it to.
The audio output was quite terrible, but eventually I came across a workaround that required updating the firmware and some boot parameters to use a different smoothing algorithm. It sounds much better now. That's pretty slow, so I had to make a fork of some of the MCP initialization code so that I can set higher speeds.
Ultimately, I wasn't able to go past 2mhz because at any speed past that, the ADCs start reporting weird truncated values. Apparently they need time to settle to get an accurate reading. There may be a workaround I'm not aware of.
At 2mhz, I'm able sample the whole keyboard about 90 times a second. Not bad, but there's room for improvement. There ought to be a way to do this purely in software and not have to route all my MIDI packets over a Audio Synthesis One might expect that electronic synthesizers would be well suited to microtonal music.
The choice to use a twelve-tone equal temperamered scale or not, after all, is simply an arbitrary implementation choice; one could imagine re-tuning the notes of a synthesizer's scale simply by adjusting some oscillators or changing some numbers that are hard-coded in software. Sadly, most synths are not designed with anything other than TET in mind. Most that provide alternate tuning tables only provide a few non-editable presets of historical tunings or whatever else the developers thought was important at the time, or they only provide a note-repeating-octave scale i.
The disinterest of synth manufacturers in JI is compounded by the limitations built into the MIDI protocol that those manufacturers have used since the 80's to make sure their products interoperate with those of their competitors. This was a noble goal, and it works great as long as your instrument is an electronic piano.
Instruments that aren't and don't function like pianos have a harder time. For instance, MIDI is limited to notes per channel which is not enough for my keyboard and it doesn't have a widely-supported way to adjust the volume of an individual note over time. Polyphonic aftertouch could be used for that, but the rare synths that support it seem to prefer to use it to add vibrato or whatever rather than as a means to control volume.
fluid dynamics - Relation between pressure, velocity and area - Physics Stack Exchange
One of my unrealized goals when I began this project was to write my own synthesizer. I could create a new MIDI-like protocol without MIDI's limitations for my keyboard to use, and then, since there aren't any available synths to speak this new protocol, I would make one.
I got as far as designing my ideal protocol and writing some code to read and write some of the commands. However, as soon as I had the electronics of the keyboard working, I wanted some quick and easy way to test it out. It turned out to work better than I expected, so that's what I've been using. I still think MIDI ought to be replaced by something better and I have strong opinions about what that "something better" ought to look like, but that's a problem I don't need to solve right now.
There's something called the MIDI tuning standardbut I think it's only supported by a handful of synths. Some synths do have ways to configure tuning tables, though.
The Emu Proteus which I have on hand is very nice in this respect in that it doesn't assume a note scale of repeating octaves; every MIDI note can be tuned indepenedently of the others, in increments of a 64th of a semitone. That's about one and a half cent s; not ideal, but probably too small to notice. Still, I would need to use mulitple channels to support the full notes with a static table. I wanted my keyboard to work with other synths besides the Proteus, and I also wanted the ability to adjust the volume of individual notes over time in response to key pressure, something that no synth I owned seemed capable of doing.