Snack manual, version 2.1

Installing Snack

Using Snack: an overview

Initializing

The beginning of a program that uses Snack might look like:

from Tkinter import *
root = Tk()

import tkSnack
tkSnack.initializeSnack(root)

# Now you can use tkSnack commands and objects
# ...

Using Sound objects

mysound = tkSnack.Sound()

Let's try reading from a file. If you're using Windows, you have at least a few WAV files sitting conveniently on your hard drive. (If you're using another operating system, you'll have to locate your own sound files to read from :-).)

mysound.read('c:/windows/media/chord.wav')

mysound.play()

tada = tkSnack.Sound(load='c:/windows/media/tada.wav')
tada.play()

You can perform a number of manipulations on the sounds objects. For example, let's tack a couple of copies of the Windows chord sound onto the end of the ta-da sound. Then we'll delete a few thousand samples from the middle of the sound (those between sample 10,000 and 40,000), and finally reverse the sound.

tada.concatenate(mysound)
tada.concatenate(mysound)
tada.play()
tada.cut(start=10000, end=40000)
tada.play()
tada.reverse()
tada.play()

tada.write('mangled-tada.au')

Audio and mixer controls

tkSnack.audio.inputDevices()
tkSnack.audio.rates()

tkSnack.audio.play_gain(30)

New canvas objects

• waveform: a raw graph of the sound data, i.e., time on the x-axis and sample amplitude on the y-axis.
• section: a power spectrum of the sound (at a given time), as calculated by Fast Fourier Transform, i.e., frequency on the x-axis and amplitude on the y-axis.
• spectrogram: a spectrogram of the sound, i.e., time on the x-axis, frequency on the y-axis, and amplitude represented by the darkness of the pixel.

c = tkSnack.SnackCanvas(root, height=400)
c.pack()
c.create_waveform(0, 0, sound=mysound, height=100, zerolevel=1)
c.create_spectrogram(0, 150, sound=mysound, height=200)

The Sound class

Options

mysound["encoding"] = "Lin32"

name =identifier

what name Tcl knows your sound under. Not terribly useful inside Python.

load =filename

specifies that the file named by filename should be read into memory after creating the sound. (Using this option allows you to use the in-memory manipulation methods of the Sound object.)

file =filename

specifies the filename of an on-disk file that should be linked to the sound. (Using this option means that many of the in-memory manipulation methods of a Sound object will not be useable.)

channel =channel-name

specifies that audio data resides on a channel which should be linked to the sound. In these cases the audio data is not loaded into memory, which is useful when playing large files or when using streaming audio. However, the Snack canvas types, e.g., waveforms, cannot be linked to sounds of these types.

frequency =integer

The sampling rate of the sound in samples per second.

channels =x

how many channels the sound uses. Values should be an integer greater than or equal to 1, or "Mono" or "Stereo".

encoding =encoding-name

Possible values for the encoding format of the sound are:

• "Lin16"
• "Lin8"
• "Lin8offset"
• "Lin24"
• "Lin32"
• "Float"
• "Alaw"
• "Mulaw"

fileformat =format-name

Current supported file formats are the following. (These formats can be read -- not all of them can be written.)

• "WAV"
• "MP3"
• "AU"
• "SND"
• "AIFF"
• "SD"
• "SMP"
• "CSL" (will usually have the extension .nsp)
• "RAW" binary

skiphead =n

is used to skip an unknown file header of length n bytes.

byteorder =string

"littleEndian" or "bigEndian"

guessproperties =boolean

specifies that Snack should try to infer properties such as byte order, sample encoding format, and sample rate for raw files by analyzing the contents of the files. Byte order is almost always detected correctly.

buffersize =integer

specifies the size of the internal buffer in samples, for channel-based sounds.

precision

specifies whether sound data should be handled using single or double precision internally.

Methods

append (binary-string)

cget (option)

mysound["encoding"]
mysound.cget("encoding")

concatenate (othersound)

configure (option=value ...)

mysound["byteorder"] = "littleEndian"
mysound.configure(byteorder="littleEndian")

copy (othersound)

crop (start=n, end=n)

data (variable=tclVariable)

destroy( )

dBPowerSpectrum ( )

filter (filter=filterobject)

flush ( )

info ( )

insert (sound=othersound, position=sample ...)

length ( )

max ( )

min ( )

pause ( )

pitch ( )

play ( )

For in-memory sounds, a number of options are available.

read (filename)

record ( )

For in-memory sounds, the append=1 option specifies that the new audio data should be appended to the end of the existing sound instead of replacing it.

For channel-based sounds, the fileformat option can be used to specify the file format to be used when writing data, since there is no filename to infer the format from.

reverse ( )

sample (sample)

# Sets the 1000th sample to 0 (of a mono sound)
mysound.sample(1000, 0)

# Sets both channels of a stero sound
mysound.sample(1000, 0, 0)

# Sets only the left channel, leaves right channel unchanged
mysound.sample(1000, left=0)

# Sets only the right channel, leaves left channel unchaged
mysound.sample(1000, right=0)

stop ( )

write (filename)

The audio object

Methods

encodings ( )

rates ( )

inputDevices ( )

playLatency ( )

pause ( )

play ( )

play_gain ( )

outputDevices ( )

record_gain ( )

selectOutput (device)

selectInput (device)

stop ( )

The mixer object

Methods

channels (line)

devices ( )

input ( )

inputs ( )

lines ( )

output ( )

outputs ( )

update ( )

volume (line)

select (device)

The Filter class

Filters in Snack are still in an early stage of development. Consult the Snack documentation for further details.

The SnackCanvas class

Waveforms

Spectrograms

Currently spectrograms have a limit of 32767 pixels.

Sections (power spectra)

Putting SnackCanvas items on regular Canvases

To accomplish this, tkSnack provides module-level versions of create_waveform, create_section, and create_spectrogram. Simply use the non-Snack canvas as the first argument. Instead of:

NonSnackCanvas.create_waveform(sound=tada)

tkSnack.create_waveform(NonSnackCanvas, sound=tada)

Last updated Mon 23 Jul 2001 13:21:20 BST