Praatchas: Praat Gotchas

An ongoing repository to help me remember some things about Praat scripting

Whitespace

Final whitespace can matter. In the example below, · represents a hidden space at the end of the line. We can guard against this gotcha by using selectObject and enclosing the object name in quotes.

select Sound Sound1
# Works

select Sound Sound1·
# Error: No object with that name. Object "Sound Sound1 " does not exist.

selectObject("Sound Sound1")
# Works

Procedures

The names of variables used inside of procedures (i.e., local variables) should begin with .:

@listSpeaker("Bart", 38)
@listSpeaker("Katja", 24)

procedure listSpeaker(.name$, .age)
    appendInfoLine("Speaker ", .name$, " is ", .age, " years old.")
endproc

Procedures are not functions; they do not return values. But you can access the local variables inside of a procedure to "return" a value from the last invocation of that procedure.

@squareNumber(5)
writeInfoLine("The square of 5 is ", squareNumber.result, ".")

procedure squareNumber(.number)
    .result = .number ^ 2
endproc

Forms

Simple Fields

Forms allow us to capture user input into variables for scripting. Here is the basic template for such a menu, where a user inputs values into fields.

form [Window Title]
    [Input Type] [Field_Description] [Default Value To Display]
    [Input Type] [Field_Description_Two] [Default Value To Display]
    # et cetera...
endform

Some gotchas to note already. The [Field_Description] is pretty-printed next to the input box as text with the underscores turned into spaces. The field description also serves as a variable name for the inputted value. You may want your the field description to start with a capital letter because that's how you like to write things. But variable names in Praat cannot start with uppercase letters. Or you may want to indicate a unit of measure in parentheses in the field description, but parentheses are also not allowed in variable names. Therefore, some care is required when determining the variable name that goes with a field description. Examples:

form Sink it
    sentence Name_of_the_ship Titanic
    real Distance_to_the_iceberg_(m) 500.0
endform

writeInfoLine(Name_of_the_ship$)
# Error: No such error (note: variables start with lower case)

writeInfoLine(name_of_the_ship$)
# "Titantic"

appendInfoLine(distance_to_the_iceberg_(m))
# Error: Unknown function <<distance_to_the_iceberg_>> in formula

appendInfoLine(distance_to_the_iceberg_)
# Error: Unknown variable

appendInfoLine(distance_to_the_iceberg)
# 500

Some Basics

Info logging

writeInfo
writeInfoLine
appendInfo
appendInfoLine
clearinfo

The commands starting with write clear the info log first. The commands ending with Line include an implicit newline$ (a special string constant like tab$). Technically, then, writeInfoLine("hello") is equivalent to clearinfo; appendInfo("hello", newline$).

writeInfoLine is the new echo. Don't use echo, print or printline anymore, I guess.

echo Hello, my name is 'name$' and I am 'age' years old.
writeInfoLine ("Hello, my name is ", name$, " and I am ", age, " years old.")

Strings

length("internationalization")
# 20

## index of first occurence of substring: 
index("internationalization", "ation")  
# 7
index ("internationalization", "x")
# 0

Concatentation and Truncation

text$ = "hallo" + "dag"
appendInfoLine(text$)
# hallodag

sound_name$ = "hallo.aifc"
textgrid_name$ = sound_name$ - ".aifc" + ".TextGrid"
appendInfoLine(textgrid_name$)
# hallo.TextGrid

Interpolation

Praat supports string interpolation where the value of a variable can be inserted into a string. For example, if file_ext$ = ".wav" then "my_recording.'file_ext$'" evaluates as my_recording.wav. Personally, I prefer concatenation over interpolation---i.e., writing something like "my_recording" + file_ext$---because it more clearly reveals how a string is constructed from strings and variables. However, numeric variables need to be coerced into strings with string$(...) in order for string concatenation to work.

The example below shows both techniques.

procedure make_id(.task$, .id_num$, .age)
	# Interpolation
	.id$ = "'.task$'_'.id_num$'_'.age'"
	# Concatenation. The numeric variable has to be converted to a string
	.alt_id$ = .task$ + "_" + .id_num$ + "_" + string$(.age)
endproc

@make_id("Listening", "001", 32)

appendInfoLine(make_id.id$)
# Listening_001_32

appendInfoLine(make_id.alt_id$)
# Listening_001_32

Control

Inline conditionals

.ext$ = if (macintosh or unix) then "WAV" else "wav" endif
appendInfoLine(.ext$)
# "wav" on a Windows computer

tjmahr / Praatchas