Managing Audio with Pd
Now, let's try a more complex example, making a patch that adds two numbers together and displays the result. Make a patch like the one shown in Figure 7, using two number boxes at the top, an object box in the middle and a number box on the bottom. Next, exit edit mode (Crtl-E again), and try changing the numbers at the top. You can do this by clicking and typing or clicking and dragging; move up to increase the number and move down to decrease it. As you've probably noticed, changing the number on the left makes the sum immediately change, but changing the number on the right does nothing. Why?
Nearly all objects in Pd treat their left-most inlet as hot, meaning that any changes in their value affects an immediate change in the output. The other inlets are cold. Changes in their values don't trigger any change in the output. The new value simply is put into storage until a computation is triggered by the hot inlet, at which point the new value is used.
But, what if you do want a change in a cold outlet to trigger a change in output? One way to accomplish this is to inset a message box. In Figure 8, I connected the outlet of the number box on the right to the inlet of a message box. The outlet of that message box then is connected to the hot inlet of the addition object box below it. When message boxes receive any message at all on their inlets, they send all their contents as a new message on their outlets. So when the right-most number box is changed, it sends a message to the bang message box, which then sends a bang message to the addition object box. Bang messages mean “Do something!”, so any object box receiving one on its hot inlet immediately performs whatever computation it's told to do. We use this behavior here to make our addition object box act as though it has two hot inlets.
But wait, doesn't that mean the bang message has to arrive after the number? If it doesn't, the patch won't work, right? Well, yes; depending on the order in which you made your connections, you already might have noticed that it doesn't. Indeed, in Figure 8 the numbers don't add up precisely because of this problem. So, we need a way to ensure that the bang message arrives after the number. An easy way to do this is to insert a delay, as shown in Figure 9. Interestingly, a delay of 0 actually works. The message simply is delayed by one DSP cycle, thus ensuring that the bang message arrives second.
The most basic audio function is input and output. The adc~ tilde object, standing for analog-to-digital converter, performs the first task; and the dac~ object, digital-to-analog converter, performs the second. Both objects operate on the first two channels by default. If you want to change this—for instance, if you have a multichannel sound card such as a Hammerfall HDSP—you can enter channel numbers as arguments, and the respective channels then are mapped to their respective inlets or outlets. Figure 10 shows a simple example where stereo input is flipped and routed to output. Because stereo input is the default, the channel numbers in the example are redundant, but we've included them anyway for demonstration purposes.
Sound data is a sequence of numbers at a specific sample rate, so it's possible to apply arithmetic operators to sound data. All you have to do instead is add a tilde to the end of the operator you want to use. For instance, Figure 11 turns a stereo signal into a mono one by adding the left and right channels together. Another useful operator is multiply, *~, which acts as a gain control. Remember, though, signals clip when output to hardware if they are beyond the values –1 and 1.
Figure 12 shows a more complex example. You might want to turn your speakers down some before you run this one, because it's loud. First, the osc~ object at the top is a sine-wave generator, in this case running at 440Hz. This signal is split into two, the left side going directly to the addition and the right side first going through a multiplication.
Now try entering –1 into the number box. The sound stops, why? If you remember your wave physics from high school, you know that waves can cancel one another out. In this case, the –1 creates a perfect inverse of the original signal. So where the original is at 1, the inverse is at –1. When you add these two signals together you get 0, silence. You also can try holding down the Shift key and dragging on the number box; the numbers should change slowly enough that you can hear the sound getting quieter as you approach –1 and then finally stopping.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide