caw/examples.md at 44256932335f696ecc4f42b23b8422ab40ae14d1

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Example 01 - Write a sine signal to an audio file.

caw programs are described using a slightly extended form of JSON. In this example the program is contained in the dictionary labeled sine_file_01 and the preceeding fields (e.g. base_dir,proc_dict,subnet_dict, etc.) contain system parameters that the program needs to compile and run the program.

{
  base_dir:    "~/src/caw/examples",
  proc_dict:   "~/src/caw/examples/proc_dict.cfg",
  mode: non_real_time,
    
  programs: {

    sine_file_01: {

      dur_limit_secs:5.0,  // Run the network for 5 seconds

      network: {

        procs: {
	  // Create a 'sine_tone' oscillator.
          osc: { class: sine_tone },
	  
	  // Create an audio output file and fill it with the output of the oscillator.
          af:  { class: audio_file_out, in: { in:osc.out } args:{  fname:"$/out.wav"} }
        } 
      }      
    }
  }
}

When executed this program will write a five second sine signal to an audio file named ~/src/caw/examples/sine_file_01/out.wav. The output file name is formed by joining the value of the system parameter base_dir with the name of the program sine_file_01.

Run the program like this:

caw example.cfg sine_file_01

caw programs specify and run a network of virtual processors. The network is described in the procs dictionary.

The line osc: { ... } defines an instance of a sine_tone processor named osc. The line af: { ... } defines an instance of a audio_file_out processor named af.

In the language of caw osc and af are refered to as processor instances or sometimes just processors.

osc and af are connected together using the in:{ ... } statement in the af instance description. The in statement connects osc.out to af.in and thereby directs the output of the signal generator into the audio file.

The args:{ ... } statment lists processor specific arguments used to create the af instance. In this case af.fname names the output file. The use of the $ prefix on the file name indicates that the file should be written to the project directory which is formed by joining base_dir with the program name. The project directory is automatically created when the program is run.

Processor Class Descriptions

processors are collections of named variables which are defined in the processor class file named by the proc_dict system parameter field.

Here are the class specifications for sine_tone and audio_file_out.

sine_tone: {
  vars: {
      srate:     { type:srate, value:0,         doc:"Sine tone sample rate. 0=Use default system sample rate"}
      ch_cnt:    { type:uint,  value:2,         doc:"Output signal channel count."},
      hz:        { type:coeff, value:440.0,     doc:"Frequency in Hertz."},
      phase:     { type:coeff, value:0.0,       doc:"Offset phase in radians."},
      dc:        { type:coeff, value:0.0,       doc:"DC offset applied after gain."},
      gain:      { type:coeff, value:0.8,       doc:"Signal frequency."},
      out:       { type:audio, flags['no_src'], doc:"Audio output" },
  }

  presets: {
      a220 : { hz:220 },
      a440 : { hz:440 },
      a880 : { hz:880 },
      mono:  { ch_cnt:1, gain:0.75 }
  }
}

audio_file_out: {
  vars: {
    fname: { type:string,               doc:"Audio file name." },
    bits:  { type:uint, value:32u,      doc:"Audio file word width. (8,16,24,32,0=float32)."},
    in:    { type:audio, flags:["src"], doc:"Audio file input." }
  }
}

The class definitions specify the names, types and default values for each variable. Since the sine_tone instance in sine_file_00 doesn't override any of the the variable default values the generated audio file must be a stereo (ch_cnt=2), 440 Hertz signal with an amplitude of 0.8.

Note that unless stated otherwise all variables can be either input or output ports for their processor. The no_src attribute on sine_tone.out indicates that it is an output-only variable. The src attribute on audio_file_out.in indicates that it must be connected to a source variable or the processor cannot be instantiated

and therefore the network it is contained by cannot be instantiated. Note that this isn't to say that it can't be an output variable - only that it must be connected.

Here is a complete list of possible variable attributes.

Attribute	Description
src	This variable must be connected to a source variable or the processor instantiation will fail.
no_src	This variable cannot be connected to a source variable (it is write-only, or output only).
init	This variable is only read at processer instantiation time, changes during runtime will be ignored.
mult	This variable may be instantiated multiple times. See `mult_input_05` below.
out	This is a subnet output variable.

caw uses types and does it's best at converting between types where the conversion will not lose information.

Here are the list of built-in types:

Type	Description
bool	true
uint	C unsigned
int	C int
float	C float
double	C double
string	Array of bytes.
time	POSIX timespec
cfg	cw object (JSON object)
audio	multi-channel audio array
spectrum	multi-channel spectrum in comlex or rect. coordinates.
midi	MIDI message array.
runtime	'no_src' variable whose type is determined by the types of the other variables. See the 'list' processor.
numeric	bool
all	This variable can be any type. Commonly used for variables which act as triggers. See the 'counter' processor.

A few type aliases are defined to help document the intended purpose of a given variable.

Type aliases:

Alias	Type	Description
srate	float	This is an audio sample rate value.
sample	float	This value is calculated from audio sample values (e.g. RMS )
coeff	float	This value will operate (e.g. add, multiply) on an audio signal.
ftime	double	Fractional time in seconds or milliseconds.

Also notice that the processor class has named presets. During processor instantiaion these presets can be used to set the initial state of the processor. See mod_sine_02 below for an example of a class preset used this way.

Example 02: Modulated Sine Signal

This example is an extended version of sine_file_01 where a low frequency oscillator (LFO) is formed using a second sine_tone processor and a sample and hold unit. The output of the sample and hold unit is then used to modulate the frequency of an audio frequency sine_tone oscillator.

Note that the LFO output is a 3 Hertz sine signal with a gain of 110 (220 peak-to-peak amplitude) and an offset of 440. The LFO output signal is therefore sweeping an amplitude between 330 and 550 which will be treated as frequency values by osc.

mod_sine_02: {

  dur_limit_secs:5.0,

  network: {

    procs: {
      lfo:   { class: sine_tone, args:{ hz:3, dc:440, gain:110 }}
      sh:    { class: sample_hold,              in:{ in:lfo.out } }
      osc:   { class: sine_tone,   preset:mono, in:{ hz:sh.out } },         
      af:    { class: audio_file_out,           in:{ in:osc.out } args:{  fname:"$/out.wav"} }
    }
  }
}

The osc instance in this example uses a preset statement. This will have the effect of applying the class preset mono to the osc when it is instantiated. Based on the sine_tone class description the osc will then have a single audio channel with an amplitude of 0.75.

In this example the sample and hold unit is necessary to convert the audio signal to a scalar value which is suitable as a coeff type value for the hz variable of the audio oscillator.

Here is the sample_hold class description:

sample_hold: {
  vars: {
    in:        { type:audio,   flags:["src"],  doc:"Audio input source." },
    period_ms: { type:ftime,   value:50.0,     doc:"Sample period in milliseconds." },
    out:       { type:sample,  value:0.0,      doc:"First value in the sample period." },
    mean:      { type:sample,  value:0.0,      doc:"Mean value of samples in period." },
  }
}

The sample_hold class works by maintaining a buffer of the previous period_ms millisecond samples. It then outputs two values based on this buffer. out is simply the first value from the buffer, and 'mean' is the average of all the values in the buffer.

Example 03: Presets

One of the fundamental features of caw is the ability to build presets which can set the network, or a given processor, to a particular state.

mod_sine_02 showed the use of a class preset to set the number of audio channels generated by the audio oscillator. presets_03 shows how presets can be specified and applied for the entire network.

In this example four network presets are specified in the presets statement and the "a" preset is automatically applied once the network is created but before it starts to execute.

If this example was run in real-time it would also be possible to apply the the presets while the network was running.

presets_03: {

  dur_limit_secs:5.0,
  preset: "a",

  network: {

    procs: {
      lfo:   { class: sine_tone, args:{ hz:3, dc:440, gain:[110 120] }},
      sh:    { class: sample_hold,    in:{ in:lfo.out } },
      osc:   { class: sine_tone,      in:{ hz:sh.out } }, 
      af:    { class: audio_file_out, in: { in:osc.out } args:{  fname:"$/out.wav"} }
    }

    presets: {
	  a: { lfo: { hz:1.0,       dc:[880 770] }, osc: { gain:[0.95,0.8] } },
	  b: { lfo: { hz:[2.0 2.5], dc:220 }, osc: { gain:0.75 } },
	  c: { lfo: a880 },
	  d: [ a,b,0.5 ]          
    }
  }
}

This example also shows how to apply args or preset values per channel.

Audio signals in caw can contain an arbitrary number of signals. As shown by the sine_tone class the count of output channels (sine_tone.ch_cnt) is up to the network designer. Processors that receive and process incoming audio will often expand the count of internal audio processors to match the count of channels they must handle. The processor variables are then automatically duplicated for each channel so that each channel can be controlled independently.

One of the simplest ways to address the individual channels of a processor is by providing a list of values in a preset specification. Several examples of this are shown in the presets contained in then network presets dictionary in presets_03. For example the preset a.lfo.dc specifies that the DC offset of first channel of the LFO should be 880 and the second channel should be 770.

Any processor variable that has multiple channels may be set with a list of values. If only a single value is given (e.g. b.lfo.dc) then the same value is applied to all channels.

Note that if a processor specifies a class preset with a preset statement, as in the osc processor in mod_sine_02, or sets initial values with an args statement, these values will be applied to the processor when it is instantiated, but may be overwritten when the network preset is applied. For example, osc will be created with the values specified in args, however when network preset "a" is applied lfo.hz will be overwritten with 1.0 and the two channels of lfo.dc will be overwritten with 880 and 770 respectively.

When a preset is specified as a list of three values then it is interpretted as a 'dual' preset. The applied value of 'dual' presets are found by interpolating between the matching values of the presets named in the first two elements of the list using the third element as the interpolation coefficient.

Preset "d" specifies an interpolation between two presets "a" and "b" where the point of interpolation is set by the third parameter, in this case 0.5. In the example the values applied will be:

variable	channel	value	equation
lfo.hz	0	1.50	a.lfo.hz[0] + (b.lfo.hz[0] - a.lfo.hz[0]) * 0.5
lfo.hz	1	1.75	a.lfo.hz[0] + (b.lfo.hz[1] - a.lfo.hz[0]) * 0.5
lfo.dc	0	550.00	a.lfo.dc[0] + (b.lfo.dc[0] - a.lfo.dc[0]) * 0.5
lfo.dc	1	495.00	a.lfo.dc[1] + (b.lfo.dc[0] - a.lfo.dc[1]) * 0.5

Notice that the interpolation algorithm attempts to find matching channels between the variables named in the presets, however if one of the channels does not exist on either preset then it uses the value from channel 0.

TODO: Check that this accurately describes preset interpolation.

Example 04 : Event Programming

program_04: {
    
  dur_limit_secs: 10.0,
	
  network {
    procs: {
	  tmr: { class: timer,                               args:{ period_ms:1000.0 }},
	  cnt: { class: counter,  in: { trigger:tmr.out },   args:{ min:0, max:3, inc:1, init:0, mode:modulo } },
	  log: { class: print,    in: { in:cnt.out, eol_fl:cnt.out }, args:{ text:["my","count"] }}
	}
  }
}

This program demonstrates how caw passes messages between processors. In this case a timer generates a pulse every 1000 milliseconds which in turn increments a modulo 3 counter. The output of the counter is then printed to the console by the print processor.

This program should output:

: my : 0.000000 : count
info: : Entering runtime.
: my : 1.000000 : count
: my : 2.000000 : count
: my : 0.000000 : count
: my : 1.000000 : count
: my : 2.000000 : count
: my : 0.000000 : count
: my : 1.000000 : count
: my : 2.000000 : count
: my : 0.000000 : count
: my : 1.000000 : count

Notice that the print processor has an eol_fl variable. When this variable receives any input it prints the last value in the text list and then a newline. In this example, although log.in and log.eol_fl both receive values from cnt.out, since the eol_fl connection is listed second in the in:{...} statement it will receive data after the log.in. The newline will therefore always print after the value received by log.in.

Example 05: Processors with expandable numbers of inputs

mult_inputs_05 extends program_04 by including a number and add processor. The number processor acts like a register than can hold a single value. As used here the number processor simply holds the constant value '3'. The add processor then sums the output of cnt and numb.

mult_inputs_05: {
    
  dur_limit_secs: 10.0,
	
  network {
    procs: {
      tmr:   { class: timer,                               args:{ period_ms:1000.0 }},
      cnt:   { class: counter,  in: { trigger:tmr.out },   args:{ min:0, max:3, inc:1, init:0, mode:modulo } },
      numb:  { class: number,                              args:{ value:3 }},
      sum:   { class: add,      in: { in0:cnt.out, in1:numb.value } },
      print: { class: print,    in: { in0:cnt.out, in1:sum.out, eol_fl:sum.out }, args:{ text:["cnt","add","count"] }}
     }
  }
}

The notable new concept introduced by this program is the concept of mult variables. These are variables which can be instantiated multiple times by referencing them in the in:{...} statement and including an integer suffix. The in variable of both add and print have the mult attribute specified in their class descriptions. In this program both of these processors have two in variables: in0 and in1. In practice they may have as many inputs as the network designer requires.

The ability to define processors with a programmable count of inputs or output of a given type is a key feature to any data flow programming scheme. For example consider an audio mixer. The count of signals that it may need to combine can only be determined from the context in which it is used. Likewise, as in this example, a summing processor should be able to form a sum of any number of inputs.

Example 06: Connecting mult inputs

This example shows how the in:{...} statement notation can be used to easily create and connect many mult variables in a single connection expression.

mult_conn_06: {

  dur_limit_secs: 5.0,

  network: {
    procs: {
      osc:    { class: sine_tone, args: { ch_cnt:6, hz:[110,220,440,880,1760,3520] }},
      split:  { class: audio_split, in:{ in:osc.out }, args: { select:[ 0,0, 1,1, 2,2 ] } },
      
      // Create merge.in0,in1,in2 by iterating across all outputs of 'split'.
      merge_a: { class: audio_merge, in:{ in_:split.out_ } },
      af_a:    { class: audio_file_out, in:{ in:merge_a.out },  args:{ fname:"$/out_a.wav" }}
      
      // Create merge.in0,in1 and connect them to split.out0 and split.out1
      merge_b:  { class: audio_merge, in:{ in_:split.out0_2 } },
      af_b:     { class: audio_file_out, in:{ in:merge_b.out },  args:{ fname:"$/out_b.wav" }}
      
      // Create merge.in0,in1 and connect them both to split.out1
      merge_c:  { class: audio_merge, in:{ in0_2:split.out1 } },
      af_c:     { class: audio_file_out, in:{ in:merge_c.out },  args:{ fname:"$/out_c.wav" }}
      
      
    }
  } 
}

The audio source for this network is a six channel signal generator, where the frequency is each channel is incremented by an octave. The split processor then splits the audio signal into three signals where the channels are distributed to the output signals based on the map given in the select list. The split processor therefore has a a single input variable in and three output variables out0,out1 and out2.

The audio_split class takes a single signal and splits it into multiple signals. The audio_merge class takes multple signals and concatenates them into a single signal. Each of the three merge processor (merge_a,merge_b,merge_c) in mult_conn_06 demonstrates three different ways of selecting multiple signals to merge in with a single in:{...} statement expression.

The goal of this example is to show that fairly complex connections between a source and destination processor can be achieved with a single in:{...} statement. This syntax results in concise network descriptions that are easier to read and modify then making lists of individual connections between source and destination variables.

Connect to all available source variables on a single source processor.

merge_a: { class: audio_merge, in:{ in_:split.out_ } },

merge_a creates three input variables (in0,in1 and in2) and connects them to three source variables (split.out0,split.out1, and split.out2). The equivalent but more verbose way of stating the same construct is: merge_a: { class: audio_merge, in:{ in0:split.out0, in1:split.out1, in2:split.out2 } }

Aside from being more compact, the only other advantage to using the _ (underscore) suffix notation is that the connections will expand and contract with the count of outputs on split should they change without having to change the code.

Connect to a select set of source variables on a single source processor.

merge_b:  { class: audio_merge, in:{ in_:split.out0_2 } },

merge_b uses the in:{...} statement begin,count notation to select the source variables for the connection. This statement is equivalent to: merge_b: { class: audio_merge, in:{ in0:split.out0, in1:split.out1 } },. This notations takes the integer preceding the suffix underscore to select the first source variable (i.e. split.out0) and the integer following the underscore as the count of successive variables - in this case 2. To select split.out1 and split.out2 the in:{...} statemennt could be changed to in:{ in_:split.out1_2 }. Likewise in:{ in_:split.out_ } can be seen as equivalent to: in:{ in_:split.out0_3 } in this example.

Connect multiple destination variable to a single source processor variable.

The begin,count notation can also be used on the destination side of the in:{...} statment expression.

merge_c:  { class: audio_merge, in:{ in0_2:split.out1 } },

merge_c shows how to create two variables merge_c.in0 and merge_c.in1 and connect both to split.out1. Note that creating and connecting using the begin,count notation is general. in:{ in1_3:split.out0_2 } produces a different result than the example, but is equally valid.

TODO:

Add the 'no_create' attribute to the audio_split.out.
What happens if the same input variable is referenced twice in an in:{} statement? An error should be generated.

Example 07: Processor suffix notiation

As demonstrated in mult_conn_06 variables are identified by their label and an integer suffix id. By default, for non mult variables, the suffix id is set to 0. Using the in:{...} statement however variables that have the 'mult' attribute can be instantiated multiple times with each instance having a different suffix id.

Processors instances use a similar naming scheme; they have both a text label and a suffix id.

proc_suffix_07: {
  dur_limit_secs: 5.0,

  network: {
    procs: {
      osc:    { class: sine_tone, args: { ch_cnt:6, hz:[110,220,440,880,1760, 3520] }},
      split:  { class: audio_split, in:{ in:osc.out }, args: { select:[ 0,0, 1,1, 2,2 ] } },

	  g0: { class:audio_gain, in:{ in:split0.out0 }, args:{ gain:0.9} },
	  g1: { class:audio_gain, in:{ in:split0.out1 }, args:{ gain:0.5} },
	  g2: { class:audio_gain, in:{ in:split0.out2 }, args:{ gain:0.2} },
	          
      merge: { class: audio_merge, in:{ in_:g_.out } },
      af:    { class: audio_file_out, in:{ in:merge.out },  args:{ fname:"$/out_a.wav" }}
    }
  } 
}

In this example three audio_gain processors are instantiated with the same label 'g' and are then differentiated by their suffix id's: 0,1, and 2. The merge processor is then able to connect to them using a single in:{...} expression, in_:g_.out which iterates over the gain processors suffix id. This expression is very similar to the merge_a connection expression in mult_conn_06: in_:split.out_ which iterated over the label suffix id's of the split.out. In this case the connection is iterating over the label suffix id's of the networks processors rather than over a processors variables.

Note also that the begin,count notation that allows specific variables to be selected can also be used here to select specific ranges of processors.

Beware however that when a processor is created with a specified suffix id it will by default attempt to connect to a source processor with the same suffix id. This accounts for the fact that the audio_gain in:{...} statements must explicitely set the suffix id of split to 0. (e.g. in:split0.out0 ). Without the explicit processor label suffix id (e.g. in:split.out0) in g1: {...} and g2: {...} the interpretter would attempt to connect to the non-existent procesor split1 and split2 - which would trigger a compilation error.