MSP Basics Tutorial 1: Test Tone - Revision history

Gtaylor@rtqe.net at 20:15, 28 June 2012

2012-06-28T20:15:41Z

Gtaylor@rtqe.net: /* Starting and stopping signal processing */

2012-06-28T20:14:52Z

‎Starting and stopping signal processing

Gtaylor@rtqe.net at 14:53, 28 June 2012

2012-06-28T14:53:33Z

Gtaylor@rtqe.net at 14:51, 28 June 2012

2012-06-28T14:51:31Z

Gtaylor@rtqe.net: /* Starting and stopping signal processing */

2012-06-28T14:27:46Z

‎Starting and stopping signal processing

Gtaylor@rtqe.net: /* Starting and stopping signal processing */

2012-06-28T14:27:24Z

‎Starting and stopping signal processing

Admin at 21:04, 25 June 2012

2012-06-25T21:04:58Z

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Admin at 03:05, 22 June 2012

2012-06-22T03:05:53Z

Admin: Created page with "Click here to open the tutorial patch: 01mTestTone.maxpat ===MSP objects are pretty much like Max objects=== MSP objects are for processing digital audio (i.e., sound) t..."

2012-06-21T20:55:16Z

Created page with "Click here to open the tutorial patch: 01mTestTone.maxpat ===MSP objects are pretty much like Max objects=== MSP objects are for processing digital audio (i.e., sound) t..."

New page

Click here to open the tutorial patch: [[01mTestTone.maxpat]]

===MSP objects are pretty much like Max objects===

MSP objects are for processing digital audio (i.e., sound) to be played
by your computer. MSP objects look just like Max objects, have inlets
and outlets just like Max objects, and are connected together with
patch cords just like Max objects. They are created the same way as
Max objects - just by placing an object box in the Patcher window
and typing in the desired name - and they co-exist quite happily with
Max objects in the same Patcher window.

===...but they're a little different.===

A patcher containing interconnected MSP objects works a little differently
from a patcher containing standard Max objects.

One way to think of the difference is just to think of MSP objects as
working much faster than ordinary Max objects. Since MSP objects need
to produce enough numbers to generate a high fidelity audio signal
(commonly 44,100 numbers per second), they must work faster than the
scheduler used by standard Max objects, which typically runs around a
thousand times per second.

Here's another helpful way to think of the difference. Think of a patch
of MSP objects not as a program in which events occur at specific
instants (as in a standard Max patch), but rather as a description
of an instrument design - a synthesizer, sampler, or effect processor.
It's like a mathematical formula, with each object constantly providing
numerical values to the object(s) connected to its outlet. At any
given instant in time, this formula has a result, which is the
instantaneous amplitude of the audio signal. This is why we frequently
refer to an ensemble of inter-connected MSP objects as a ''signal network''.

So, whereas a patch made up of standard Max objects sits idle and does
nothing until something occurs (a mouse click, an incoming MIDI
message, the clock firing on a {{maxword|name=metro}} object, etc.) causing
one object to send a message to another object, a signal network of
MSP objects, by contrast, is always active (from the time it's turned
on to the time it's turned off), with all its objects constantly
communicating to calculate the appropriate amplitude for the sound at
that instant.

===...so they look a little different===

The names of all MSP objects end with the tilde character (''~'').
This character, which looks like a cycle of a sine wave, just serves
as an indicator to help you distinguish MSP objects from other
Max objects.

The patch cords between MSP objects have stripes. This helps you
distinguish the MSP signal network from the rest of the Max patch.

[[Image:images/basicchapter01a.png|border]]
MSP objects are connected by striped patch cords''

Take a look at the tutorial patcher. You'll see that we have six
items of our patcher's canvas. Three of them should be familiar
to you: we've got a Max {{maxword|name=comment}} box ("warning:loud") and
two {{maxword|name=message}} boxes labelled <code>start</code> and <code>stop</code>.
The bulk of the patcher logic consists of three objects we've
never seen before: a {{maxword|name=cycle~}} object, an {{maxword|name=ezdac~}} object,
and something that looks suspiciously like a {{maxword|name=slider}} object
but is actually a {{maxword|name=gain~}} object. Let's look at these objects
in turn, starting with the {{maxword|name=dac~}} at the bottom of the patcher
and returning from there to the top of the chain.

===Digital-to-analog converter: ezdac~===

''The digital-to-analog converter'' (DAC) is the part of your computer
that translates the stream of discrete numbers in a digital audio signal
into a continuous fluctuating voltage which will drive your loudspeaker.

Once you have calculated a digital signal to make a computer-generated
sound, you must send the numbers to the DAC. So, MSP has an object
called {{maxword|name=ezdac~}}. This object is generally the terminal object in
any signal network, and is required for any signals generated by MSP
to make it out of your computer as sound. The {{maxword|name=ezdac~}} object receives
the signals you wish to hear in its inlets, and has a stereo configuration
talking to the first two channels of your audio hardware - this is why there
are two inlets on the {{maxword|name=ezdac~}}
in our patcher. If you were using more elaborate audio output hardware that
required more than two channels, you would use the {{maxword|name=ezdac~}} object's
cousin the {{maxword|name=dac~}} object, which lets you specify other audio
channels as outlets using typed-in arguments.

'''Important!''' {{maxword|name=dac~}} must be receiving a signal of non-zero
amplitude in order for you to hear anything. {{maxword|name=dac~}} expects to
receive signal values in the range -1.0 to 1.0. Numbers that exceed
that range will cause distortion when the sound is played.

===A simple wavetable oscillator: cycle~===

The best way to produce a periodic waveform is with {{maxword|name=cycle~}}.
This object uses the technique known as ‘wavetable synthesis’. It
reads through a list of 512 values at a specified rate, looping back
to the beginning of the list when it reaches the end. This simulates
a periodically repeating waveform.

You can direct {{maxword|name=cycle~}} to read from a list of values that you
supply (in the form of an audio file), or if you don't supply one,
it will read through its own table which represents a cycle of a
cosine wave with an amplitude of 1. We'll show you how to supply
your own waveform in a later tutorial; for now we'll use the cosine
waveform.

[[Image:images/basicchapter01b.png|border]]
''Graph of 512 numbers describing one cycle of a cosine wave with amplitude 1''

The {{maxword|name=cycle~}} object receives a frequency value (in Hz) in its left
inlet, and it determines on its own how fast it should read through the
list in order to send out a signal with the desired frequency.

----
'''Technical detail: '''To figure out how far to step through the list
for each consecutive sample, {{maxword|name=cycle~}} uses the basic formula

I=ƒL/R

where ''I'' is the amount to increment through the list, ''ƒ''
is the signal's frequency, ''L'' is the length of the list (512 in
this case), and ''R'' is the audio sampling rate. {{maxword|name=cycle~}}
is an ‘interpolating oscillator’, which means that if ''I'' does
not land exactly on an integer index in the list for a given sample,
the {{maxword|name=cycle~}} object interpolates between the two closest numbers
in the list to find the proper output value. Performing interpolation in a wavetable
oscillator makes a substantial improvement in audio quality. The {{maxword|name=cycle~}}
object uses linear interpolation, while other MSP objects use very high-quality (and
more computationally expensive) polynomial interpolation.
----

The {{maxword|name=cycle~}} object has a default frequency of 0 Hz. So in order
to hear the signal, we need to supply an audible frequency value. This
can be done with a number argument as in the example patch, or by
sending a number in the left inlet, or by connecting another MSP object
to the left inlet. If we listen to the output of this signal with its
frequency set in an audioble range, we should hear a sine wave, the purest
(in terms of spectrum) sound that we can make.

===A volume control: gain~===

If we were to directly connect our {{maxword|name=cycle~}} object to a {{maxword|name=dac~}}
object and start the audio, we could easily damage our speakers or, more
importantly, our ears. MSP objects that generate audio (such as {{maxword|name=cycle~}})
generally do so at a normalized dynamic range of -1 to 1, which the {{maxword|name=dac~}}
object will interpret as being the loudest signal possible. To avoid
these dangers, it's important to have an object in-between to control
the amplitude of the signal going to our speakers. The {{maxword|name=gain~}}
slider performs just such a function:

[[Image:images/basicchapter01c.png|border]]
The {{maxword|name=gain~}} slider in the Explorer

The {{maxword|name=gain~}} slider ''multiplies'' its incoming signal by a
factor based on the position of the slider which, for all but the
uppermost reaches of the object, is a number less than 1. As a result,
the {{maxword|name=gain~}} object almost always ''attenuates'' (or turns down)
the volume of what comes in, much like a fader on an analog mixing
desk. The {{maxword|name=gain~}} object is in several ways a graphical version
of a {{maxword|name=*~}} object, which we'll look at in a later tutorial.

===Starting and stopping signal processing===

In this set of tutorials, we're using the {{maxword|name=ezdac~}} object to turn audio
off and on our patches. While it's great to be able to click on the icon and to see
whether or not audio is on in the Patcher window, the The {{maxword|name=ezdac~}} object
is hard-wired to output channels 1 and 2 on your audio device, which might not
make it appropriate for working with multi-channel sound. For our tutorials,
however, it should be fine.

The {{maxword|name=ezdac~}} object is one of five MSP objects (along with {{maxword|name=adc~}},
{{maxword|name=ezadc~}} and {{maxword|name=ezdac~}}, and {{maxword|name=adstatus}}) that can turn on and off the MSP audio
network from ''within'' your patcher. There are two common ways of turning audio on and off used in these tutorials - by clicking on the {{maxword|name=ezdac~}} object in a patch, or sending a <code>1</code> or <code>0</code> to the left inlet of a {{maxword|name=ezdac~}} object (or an {{maxword|name=ezadc~}} object).

'''Important!''' Since you generally don't want to
enable or disable processing for '''all'''
open signal networks in '''all''' currently open Max patchers (which might
mean you'd hear things you don't expect) the {{maxword|name=ezdac~}} object
has an attribute called ''local'' which can be set using the Inspector. When
the ''local'' attribute is enabled, turning audio on or off will only affect
the local Max patch (and its subpatches).

[[Image:images/localattribute.png|border]]

Although {{maxword|name=ezdac~}} is part of a signal network, it also understands
certain Max messages, such as <code>0</code> and <code>1</code>. Many MSP
objects function in this manner, accepting certain Max messages as
well as audio signals.

===Listening to the Test Tone===

The first time you start up Max, it will try to use your computer's
default sound card and driver (CoreAudio on Macintosh or MME on Windows)
for audio input and output. If you have the audio output of your computer
connected to headphones or an amplifier, you should hear the output of
MSP through it. If you don't have an audio cable connected to your
computer, you'll hear the sound through the computer's internal speaker.

In order to get MSP up and running properly, we recommend that you start
the tutorials using your computer's built-in sound hardware. If you
want to use an external audio interface or sound card, please refer to
the Audio Input and Output chapter for details on configuring MSP to
work with audio hardware.

* Set your audio amplifier (or amplified speakers) to their minimum
setting, then click on the {{maxword|name=ezdac~}} object in the tutorial
patcher. Click and drag on the {{maxword|name=gain~}} slider until it's set to
somewhere in the middle of its length. Adjust your audio amplifier to
a comfortable setting. Once you're satisfied that the patcher is working,
click on the {{maxword|name=ezdac~}} object to turn off that annoying test tone.

===Troubleshooting===

If you don't hear any sound coming from your computer when you click on
the {{maxword|name=ezdac~}} in this example and turn up the {{maxword|name=gain~}} slider,
check the level setting on your amplifier or mixer, and check all your
audio connections. Check that the sound output isn't currently muted.
On Macintosh, the sound output level is set using the Sound preferences
in the System Preferences application. On Windows, the sound output
level is set using the Sounds and Audio Devices setup
(Start - Control Panels - Sounds and Audio Devices).

If you are still are not hearing anything, choose '''Audio Status''' from
the Options Menu and verify that the Core Audio Built in Controller
for Macintosh or MME driver for Windows is selected in the Driver
pop-up menu. If it isn't, choose it.

[[Image:images/basicchapter01d.png|border]]

===Summary===

A ''signal network'' of connected MSP objects describes an audio
instrument. The digital-to-analog converter of the instrument is represented
by the {{maxword|name=ezdac~}} object; {{maxword|name=ezdac~}} must be receiving a signal of non-zero
amplitude (in the range -1.0 to 1.0) in order for you to hear anything.
The {{maxword|name=cycle~}} object is a wavetable oscillator which reads cyclically
through a list of amplitude values, at a rate determined by the
supplied frequency value. Signal processing is turned on and off by clicking on the
object or by sending a <code>1</code> or <code>0</code> message to it.

===See Also===

{{maxword|name=cycle~}} - Table lookup oscillator

{{maxword|name=gain~}} - Exponential scaling volume slider

{{maxword|name=ezdac~}} - Audio output and on/off

[[Category:Teaching Material]]

@@ Line 77: / Line 77: @@
 '''Important!''' Since you generally don't want to  enable or disable processing for '''all''' open signal networks in '''all''' currently open Max patchers (which might mean you'd hear things you don't expect) the {{maxword|name=ezdac~}} object has an attribute called ''local'' which can be set using the Inspector. When the ''local'' attribute is enabled, turning audio on or off will only affect the local Max patch (and its subpatches).
-[[File:Localattribute.png|border]]
+[[Image:Localattribute.png|border]]
 Although {{maxword|name=ezdac~}} is part of a signal network, it also understands certain Max messages, such as <code>0</code> and <code>1</code>. Many MSP objects function in this manner, accepting certain Max messages as well as audio signals.

@@ Line 77: / Line 77: @@
 '''Important!''' Since you generally don't want to  enable or disable processing for '''all''' open signal networks in '''all''' currently open Max patchers (which might mean you'd hear things you don't expect) the {{maxword|name=ezdac~}} object has an attribute called ''local'' which can be set using the Inspector. When the ''local'' attribute is enabled, turning audio on or off will only affect the local Max patch (and its subpatches).
-[[Image:Localattribute.png|border]]
+[[File:Localattribute.png|border]]
 Although {{maxword|name=ezdac~}} is part of a signal network, it also understands certain Max messages, such as <code>0</code> and <code>1</code>. Many MSP objects function in this manner, accepting certain Max messages as well as audio signals.

← Older revision		Revision as of 14:53, 28 June 2012
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−	Click here to open the tutorial patch: [[~~File~~:01mTestTone.maxpat]]	+	Click here to open the tutorial patch: [[Media:01mTestTone.maxpat]]

	===MSP objects are pretty much like Max objects===		===MSP objects are pretty much like Max objects===

← Older revision		Revision as of 14:51, 28 June 2012
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−	Click here to open the tutorial patch: [[01mTestTone.maxpat]]	+	Click here to open the tutorial patch: [[File:01mTestTone.maxpat]]

	===MSP objects are pretty much like Max objects===		===MSP objects are pretty much like Max objects===

@@ Line 77: / Line 77: @@
 '''Important!''' Since you generally don't want to  enable or disable processing for '''all''' open signal networks in '''all''' currently open Max patchers (which might mean you'd hear things you don't expect) the {{maxword|name=ezdac~}} object has an attribute called ''local'' which can be set using the Inspector. When the ''local'' attribute is enabled, turning audio on or off will only affect the local Max patch (and its subpatches).
-[[Image:images/Localattribute.png|border]]
+[[Image:Localattribute.png|border]]
 Although {{maxword|name=ezdac~}} is part of a signal network, it also understands certain Max messages, such as <code>0</code> and <code>1</code>. Many MSP objects function in this manner, accepting certain Max messages as well as audio signals.

@@ Line 52: / Line 52: @@
 distinguish the MSP signal network from the rest of the Max patch.
-[[Image:images/basicchapter01a.png|border]]
+[[Image:Basicchapter01a.png|border]]
 MSP objects are connected by striped patch cords''
@@ Line 105: / Line 105: @@
 waveform.
-[[Image:images/basicchapter01b.png|border]]
+[[Image:Basicchapter01b.png|border]]
 ''Graph of 512 numbers describing one cycle of a cosine wave with amplitude 1''
@@ Line 149: / Line 149: @@
 slider performs just such a function:
-[[Image:images/basicchapter01c.png|border]]
+[[Image:Basicchapter01c.png|border]]
 The {{maxword|name=gain~}} slider in the Explorer
@@ Line 181: / Line 181: @@
 the local Max patch (and its subpatches).
-[[Image:images/localattribute.png|border]]
+[[Image:Localattribute.png|border]]
 Although {{maxword|name=ezdac~}} is part of a signal network, it also understands
@@ Line 226: / Line 226: @@
 pop-up menu. If it isn't, choose it.
-[[Image:images/basicchapter01d.png|border]]
+[[Image:Basicchapter01d.png|border]]
 ===Summary===