Pd Documentation chapter 3: Getting Pd to run

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How to get Pd up and running depends on your operating system. Pd runs under Irix, Windows, and Linux. You must first get and install it, and then untangle whatever problems arise in handling audio and MIDI input and output, and finallyget Pd to meet its real-time obligations reliably.

3.1. how to get and install Pd

3.1.1. IRIX (SGI machines)

Download Pd, which will be a "tar.Z" file. You can unpack this by typing "zcat [name].tar.Z | tar xf -" to a shell. This creates a directory named "pd".

Starting with release 0.25, Pd should come in "n32" and "o32" versions. "o32" is the default and will run on IRIX 5.x and up. "n32" runs faster, but only on 6.x and up. Also, "externs" have to be updated for n32. The "pd" executable (bin/pd in the distribution) is a symbolic link to either "pd-o32" or "pd-n32."

Please note that the path to the Pd executable program can't contain space characters; don't put it in a directory named "Program Files" for example.

If for example you put Pd in ~, the executable program will be ~/pd/bin/pd. The program looks at its command line to figure out where it is, so it's best to invoke Pd by its full pathname. You should always invoke Pd from a Unix shell because many important messages appear on the standard error.

The simplest way to invoke Pd is to make an alias in your ".cshrc" file (assuming you use the "c" shell) such as:


    alias pd ~/pd/bin/pd

(assuming your Pd distribution landed in ~, for example).

Pd will open the "default" audio input and output devices, without regard for whether they are in sync or not. This will be bad if they aren't; use the "-noadc" or "-nodac" flag to disable either the input or output. Pd is supposed to handle up to 8 channels of audio in and/or out. (But at least one user had to recompile Pd on his Onyx to get 8 channels working.)

As to MIDI, Pd simply attempts to open all available MIDI devices for input and output, which is probably very bad on anything more recent than my Indy. If any MIDI ports fail to open either for input or output, all MIDI is disabled.

Pd has not been fixed to request real-time priority from Irix; it will compete with all other processes on your machine for CPU time.

3.1.2. Microsoft Windows

Pd is compiled under NT, but sort of works under windows 95/98 as well. Pd will appear as a "zip" file. Unzip this, creating a directory such as \pd. (You can put it wherever you like but the path should have no spaces in it; so "Program Files" would be a bad place.)

If for example you put Pd in C:\pd, the executable program will be C:\pd\bin\pd. You can simply adjust your path to include C:\pd\bin and just invoke "pd" in a command prompt window. You can also make a "command prompt" shortcut to start Pd.

3.1.2.1. The special joys of Windows 95

On Windows 95 you can expect a hard time. Every user who tries it seems to encounter a new problem. The best way to run Pd is to get into the "MSDOS Prompt" program and type \pb\bin\pd to it (or whatever the path ends up being.) You can probably put pd's "bin" directory in your path so that you just type "pd" to the prompt.

You don't want to run Pd from the "run" menu because if it fails to start up the window holding the error message will disappear instantly. Ditto for clicking on "batch files" or on the Pd executable itself.

The most common reason Pd might fail to start up in W95 is not having "networking" turned on. Pd is actually two programs that establish an IP interconnection. Beware that this sometimes fools Windows into calling your ISP for no reason.

It is often necessary to specify a huge audio buffer to get steady audio output in W95; see the command line arguments below.

3.1.3. Linux

What to do may depend on which flavor of Linux you are running (e.g., Debian or Red Hat) and on where you got Pd from (Miller or Guenter). The instructions here should work for Pd 0.26 and up regardless of your situation, but if you have any trouble just mail msp@ucsd.edu and I'll try to figure out what's wrong and update the instructions accordingly.

Before you start, you might want to check that you have the resources Pd needs. You can verify that you've got TK installed by typing, "wish" to a shell window. If you've got X windows running, I think it's almost certain that you also have TK. If you don't at least have the X client side up, you won't be able to run Pd. If you want to be able to compile your own Pd objects, you should also check that you have a C compiler by typing "gcc" to a command line. If you want to recompile Pd itself, you'll also need the X client developer package, which isn't installed by default on Red Hat at least; the package name is XFree86-devel.

Next try to get MIDI and audio working on your computer (see the next section). I don't know what software functions best as a test program; I use Pd but if you're reading this you might not be sure your copy of Pd is working yet.

Download Pd, perhaps from http://www.crca.ucsd.edu/~msp/software.html giving a file such as "pd-linux-026.tar.gz". Open a "shell" window, cd to the directory containing the file, and type the command,

    zcat pd-linux-026.tar.gz | tar xf -
which creates a directory named "pd". I use my home directory. Then if you use "bash" put the line,
alias pd=~/pd/bin/pd
in the file ".bashrc" in your home directory. You can add options such as,
    alias "pd=/home/me/pd/bin/pd -path /home/me/pdlib"
to have Pd automatically search for files in /home/me/pdlib, for example. If you use the C shell (csh), you edit the .cshrc file and use the less painful syntax,
    alias pd ~/pd/bin/pd -path ~/pdlib
Then type ". .bashrc" or "source .cshrc" to make the change, and type "alias" to check that it happened. (you don't have to retype the "source" command for new shells; they run the "rc" file automatically.)

Next type,

    pd -nosound
If this works, you'll see the Pd window appear. Quit and go to the next paragraph. If this doesn't work, it could be because you're missing TK or even X windows, or more likely, that Pd isn't able to find its own files. This could either mean that you aren't invoking Pd by its full path name, or you're using a symbolic link, or there are spaces in Pd's path, or that the files somehow got moved around.

Next try audio. We want to know whether audio output works, whether audio input works, and whether they work simultaneously. First run "aumix" to see audio input and output gains and which device is "recording". Then test audio output by running

    pd -noadc
and selecting "test audio and MIDI" from the "help" menu. You should see a patch. Turn on the test tone and listen. Do the usual where's-the-signal business.

Then quit Pd and test audio input via

    pd -nodac
Re-open the test patch and hit "meter"; look at the levels. 100 dB is a hard clip; arrange gains so that the input signal tops out around 80 or 90, but no higher.

Now see if your audio driver can do full duplex by typing "pd" with no flags. If you see error messages involving /dev/dsp or /dev/dsp2, you're probably not able to run audio in and out at the same time. If on the other hand there's no complaint, and if the audio test patch does what you want, you might wish to experiment with the "-audiobuffer" flag to see what values of audio latency your audio system can handle.

3.2. audio and MIDI support

Pd comes with multichannel audio support for IRIX, Windows, and Linux; on IRIX this should work without any trouble at all, but on the other two you have to be aware of many potential complications.

You may be interested in getting only audio output or audio input, or you may need both to run simultaneously. By default, Pd will try to run both, but if you don't need either input or output, you may find that Pd runs more reliably, or at least more efficiently, with the unused direction turned off. This is controlled by Pd's command line flags.

Depending on your application you will have a more or less stringent latency requirement. Ideally, when any input (audio, MIDI, keyboard, network) is available, the outputs (in particular the audio output) should react instantly. In real life, it is necessary to buffer the audio inputs and outputs, trying always to keep some number of milliseconds ahead of real time to prepare for the inevitable occasions where the CPU runs off to service some different task from Pd. How small this latency can be chosen depends on your OS and your audio driver.

To test audio and MIDI, start Pd and select "test Audio and MIDI" from the "help" menu.

TIP: If Pd starts up but you get distortion or glitches in the audio output, this could be either because the "audio I/O buffer" isn't big enough, or else because the CPU load of the patch you're running is too great for the machine you have, or else because the ADC and DAC are out of sync or even at different sample rates. To test for the first possibility, try increasing the "-audiobuf" parameter in the command line (but see also under your OS below.) For the second, start up your favorite performance monitor program; and for the third, try starting Pd up with ADCs disabled.

3.2.1. IRIX (SGI machines)

Pd takes command line arguments to set the number of input and output channels and the sample rate. These don't affect the SGI's audio settings, which you have to set separately using the "audio panel." Pd does detect the audio sample rate if you don't specify one on the command line.

On SGI machines, you have to work to get MIDI running. Before you start Pd, verify that least one MIDI port is configured open. Pd opens the FIRST MIDI port that's open. You might want to get rid of the "software" MIDI port if you're running 6.x. On Indys, the usual practice is to open serial port number 2 because some systems configure port 1 as "console" by default. You can use the GUI if you want, or else just type


    startmidi -d /dev/ttyd2

to get port 2 speaking MIDI, and

    stopmidi

to stop it. You can test whether MIDI is configured by typing,

    ps -dafe | grep midi

and looking for "startmidi" processes.

It's a good idea to connect your serial port to your MIDI interface before typing the "startmidi" command, not afterward, at least in 5.x. We use the Opcode Studio 3 interface but in principle any Mac-compatible one should work.

The O2 apparently has RS232 ports, not RS422. I think SGI's web site says something about how to deal with this.

3.2.2. Windows/NT (PC compatibles)

On Pcs, you can ask for a list of audio and MIDI devices by typing "pd -listdev"; you can then specify which audio and MIDI device to use. Type "pd -help" (or make any mistake) to get the syntax for specifying which device to use.

Most PC sound cards seem to have MIDI built in; you don't seem to have to do anything special to get Pd to send and receive MIDI. You can list and choose MIDI devices in the same way as audio.

MIDI timing is very poor if you are using simultaneous audio input and output; if you suppress either audio input or output things will improve somewhat under NT; you can apparently get the jitter down to ~40 msec. On W95 performance is simply terrible. W98, with either audio input or output suppressed, offers fairly good MIDI timing (~5 msec jitter) but crashes occasionally.

Some NT and W98 drivers greet you with a constant trail of "resyncing audio" messages. Sometimes you can fix this by invoking Pd with the "-noresync" flag.

3.2.3. Linux (PC compatibles and Alpha)

Be forewarned: installing and testing audio and MIDI drivers in Linux can take days or weeks. There apears to be no single place where you can get detailed information on Linux audio. In addition to the information here, you should see what's posted on Guenter's page, http://gige.epy.co.at/ .

Depending on your hardware and software, you might or might not be able to run "full duplex," i.e., use audio input and output at the same time. For many applications it's important to be able to do this, but if by any chance you don't need simultaneous input and output you will have much less trouble than if you do.

There are two widely-used driver sets, called "OSS" and "ALSA". OSS is included in the standard Linux kernels since version 2.2. However, for some audio cards you can find newer versions than are included in the kernel releases. You can get ALSA from http://www.alsa-project.org/ .

There is also a commercial version of the OSS drivers which costs $30 (slightly more for certain audio cards.) Hit http://www.opensound.com/ . There are more supported cards in commercial OSS than in free OSS.

The ALSA driver set is compatible with OSS so that you can run OSS programs with ALSA installed. You can run Pd this way; but you must run Pd with a "-frags" flag as described below.

3.2.3.1. Installing OSS

On the Red Hat distribution at least, OSS is started using the "sndconfig" program. It's harder to stop it. You can see if the audio drivers are running using "lsmod" (as root.) If you see something like:


Module         Pages    Used by
eepro100           3            1 (autoclean)
opl3               3            0
opl3sa2            1            0
ad1848             4    [opl3sa2]       0
mpu401             5    [opl3sa2]       0
sound             15    [opl3 opl3sa2 ad1848 mpu401]    0
soundcore          1    [sound] 6
soundlow           1    [sound] 0
aic7xxx           23            2

then OSS is running, and if all you see is:

eepro100           3            1 (autoclean)
aic7xxx           23            2

then it isn't. You can turn OSS off by running "rmmod" repeatedly, starting with "opl3" (or whatever) so as not to remove any module before you remove all the modules that depend on it. In the above listing, "opl3*" is device dependent and you might see different names.

The file, "/etc/conf.modules" apparently controls which sound drivers are started at boot time. The sndconfig program updates this file but you can also change things manually, for instance to switch between two different sound cards.

3.2.3.2. ALSA

ALSA is newer, hence less stable and harder use, than OSS. Some multichannel cards support only ALSA and not OSS (and ALSA's OSS emulation is apparently stereo only.)

You have to install the "driver", "library", and "utils" distributions from the Alsa site. The file, "INSTALL" in the ALSA driver distribution should describe how to install ALSA.

By default, Pd uses OSS. If you are running ALSA, it will use ALSA's OSS emulation. To make Pd use ALSA "natively", i.e., the way ALSA is designed to be used, include the "-alsa" flag in the command line.

3.2.3.3. stream and block mode (-frags flag)

Under either OSS or ALSA, programs can stream sound using either "block" or "stream" mode. Stream mode is the more modern and better of the two. Pd uses stream mode by default.

In OSS at least, certain drivers don't support stream mode but support block mode. The symptom of this is usually "audio stuck" messages. You can force Pd to use block mode by specifying " -frags" and/or "-fragsize" flags (default, 4 and 11). This causes Pd to ignore its "audiobuf" argument which in Linux is relevant only to stream mode.

In the "frags" model, Pd's input and output buffers are divided into a number of fragments of a given size. The "fragsize" argument is by powers of 2, so that "11" means 2048-byte fragments, which is 512 sample frames, or about 11.6 msec at 44100 Hz. So "-frags 4 -fragsize 11" gives an audio latency around 46 msec.

In particular, if your machine is running ALSA drivers but you want to run Pd in OSS emulation, you probably will have to specify "-frags". The "-fragsize" specification isn't available for ALSA; it's always 64 sample frames so "-frags 10" specifies about 15 msec latency.

3.2.3.4. which sound card?

Here's a rundown on my experiences with sound cards so far. See also Guenter's audio page.

opl3sa

This is the "Yamaha" audio system. It comes on many Dell machines and seems to offer reasonable consumer quality audio, at least under NT. I believe the current version of OSS can get full duplex operation out of an OPL3sa audio system.

The opl3sa2 in particular is an ISA device and you have to deal with I/O addresses and all that.

You might well have to do the "-frags" thing (see above) with oplxxx.

cs4232

The 1999 vintage dual-processor Dell machines have "cs4232" audio, which I couldn't get working.

es1370 (Creative PCI128)

Guenter has the best info on this card at http://gige.epy.co.at/ .

(CAUTION -- newer Creative PCI128s are actually SBLive inside... get a generic one to be sure.)

The es1370 is the chip. There are other cheap audio cards that sport es1370s. Apparently the audio quality isn't great, but on the other hand, you can actually get it to output 4 independent channels---I've tried it an it worked. Street price for a PCI128 in the USA is $30.

The audio inputs and outputs on my PCI128 aren't clearly labelled and various documents give them inconsistent names. On my card there are 4 stereo mini jacks and a joystick port, in this order:

joystick    black            green       red       blue
            bidirectional    line-out    mic-in    line-in
I think you can load the es1370 driver on the fly simply by typing
    modprobe es1370
(perhaps after running "rmmod" on some other driver as described above.) To have your computer automatically load es1370 on startup, put the lines,
    alias sound es1370
    pre-install sound insmod sound dmabuf=1
    alias midi es1370
in /etc/conf.modules, or run sndconfig (as root) and get it to do it somehow.

To make the card do quad you have to download and compile Guenter's es1370 control program, which is part of the "small patch" you can download from http://gige.epy.co.at/pd/cards.html .

The really tricky thing about quad is that the regular "stereo" outputs move to the black jack and the new "back" channels appear on the regular line output (green.) What's more, the back channels are normally mixed into the front ones (or is it vice versa?) so you'll have to play blind man's bluff with aumix for an hour or so to get the four channels to emerge separately.

My own version of Guenter's control program can be downloaded from http://www.crca.ucsd.edu/~msp/Software/audio-es1370.tar.gz.

I believe I have the ALSA driver also working with es1370 now (0.31).

Creative SBLive

There is an OSS driver in the standard Linux distribution, but it doesn't support selecting for incoming MIDI so Pd will not see and MIDI input from it. If you need MIDI, you must install ALSA; still, it's best to run Pd with ALSA emulating OSS, just specifying "-frags."

Sonorus Stud I/O

This $1000 card is supposed to do multichannel digital I/O in Linux, via a beta version of a commercial OSS driver ($40). Sonorus's web site proclaims a new product called the "MedI/O" to appear shortly.

RME 9652 (Hammerfall)

Winfried Ritsch has written a Linux driver for the RME9652 (3 ADATs and one AES/EBU, all in and out simultaneously and in sync). They cost slightly under $500. I've got one running with Pd. The driver works only with uniprocessor Linux. DO NOT CONFUSE THE 9652 WITH OTHER RME BOARDS WHICH MIGHT NOT WORK WITH PD.

Hit http://www.crca.ucsd.edu/~msp/Software/audio-rme.tar.gz for my version of Winfried's driver and test program which works with the current release of Pd (0.27).

With this card there is no FIFO size control at all within Pd; it's set using Winfried's test program. As far as I know the RME9652 is the only professional audio hardware you can run with Pd.

With the RME option, you can use "-soundindev" and "-soundoutdev" flags to select which input and output devices to use (for instance, the AES/EBU ports are devices 25/26).

Word has it that Hammerfalls now have an ALSA driver; from what I hear it won't work yet with Pd...

MIDIMAN

Midiman sells devices with between 4 and 12 analog channels in and out, for which there are ALSA drivers. I have tested Pd (0.31test4) with one and it worked fine.

3.3. graphics rendering using GEM

Mark Danks's GEM package is available from http://www.danks.org/mark . Download this to extend Pd to do 3-d graphical rendering using Open GL

3.4. starting Pd

Pd is a "command line" program. The best way to run it is from your "terminal emulator," "shell," or "MSDOS prompt." The command line is:

    pd [options] [patches to open]

although you may have to specify a path so your command interpreter can find Pd (OS dependent.) The options are as follows:

-r            -- specify sample rate
-inchannels   -- number of audio input channels (0-8)
-outchannels  -- number of audio output channels (0-8)
-audiobuf     -- specify size of audio buffer in msec
-sleepgrain   -- specify number of milliseconds to sleep when idle
-nodac           -- suppress audio output
-noadc           -- suppress audio input
-nosound         -- suppress audio input and output
-nomidiout       -- suppress MIDI output
-nomidiin        -- suppress MIDI input
-nomidi          -- suppress MIDI input and output
-path      -- add to file search path
-open      -- open file(s) on startup
-lib       -- load object library(s)
-font         -- specify default font size in points
-verbose         -- extra printout on startup and when searching for files
-d            -- specify debug level
-noloadbang      -- suppress all loadbangs
-nogui           -- suppress starting the GUI
-guicmd "cmd..." -- substitute another GUI program (e.g., rsh)
-send "msg..."   -- send a message
with additional options for NT:

-listdev          -- list audio and MIDI devices
-soundindev    -- specify audio input device number
-soundoutdev   -- specify audio output device number
-midiindev     -- specify MIDI input device number
-midioutdev    -- specify MIDI output device number

and for Linux:

-rt or -realtime -- real time priority (superuser or setuid only)
-frags        -- specify number of audio fragments (defeats audiobuf)
-fragsize     -- specify audio fragment size
-alsa            -- use ALSA audio drivers
-alsadev      -- specify ALSA I/O device number (counting from 1)
-rme             -- use RME 9652 audio drivers
-soundindev   -- specify RME input device number (counting from 1)
-soundoutdev  -- specify RME output device number 

Here are some details on some of the audio options (but see also the next section on file management.)

3.4.1. sample rate

The sample rate controls Pd's logical sample rate which need not be that of the audio input and output devices. If Pd's sample rate is wrong, time will flow at the wrong rate and synthetic sounds will be transposed. If the output and input devices are running at different rates, Pd will constantly drop frames to re-sync them, which will sound bad. You can disable input or output if this is a problem.

3.4.2. audio buffer size

You can specify an audio buffer size in milliseconds, typically between 10 and 300, depending on how responsive your OS and drivers are. If this is set too low there will be audio I/O errors ("data late"). the higher the value is, on the other hand, the more throughput delay you will hear from the audio and/or control inputs (MIDI, GUI) and the audio coming out.

3.5. dealing with files

Pd has a search path feature; you specify the path on the command line using the "-path" option. Paths may contain any number of files. If you specify several files in a single "-path" option they're separated by colons in unix or semicolons in NT. When Pd searches for an abstraction or an "extern" it uses the path to try to find the necessary file. The "read" messages to qlists and arrays (aka tables) work the same way.