Audio¶
This module allows you to play your own sounds. If you are using a micro:bit
V2, audio
is also part of the microbit
module.
By default sound output will be via the edge connector on pin 0 and the built-in speaker V2. You can connect wired headphones or a speaker to pin 0 and GND on the edge connector to hear the sounds.
Functions¶
-
audio.
play
(source, wait=True, pin=pin0, return_pin=None)¶ Play the source to completion.
- source:
Sound
- Themicrobit
module contains a list of built-in sounds that your can pass toaudio.play()
. - source:
AudioFrame
- The source agrument can also be an iterable ofAudioFrame
elements as described below. - wait: If
wait
isTrue
, this function will block until the source is exhausted. - pin: An optional argument to specify the output pin can be used to
override the default of
pin0
. If we do not want any sound to play we can usepin=None
.- return_pin: specifies a differential edge connector pin to connect to an external speaker instead of ground. This is ignored for the V2 revision.
- source:
-
audio.
is_playing
()¶ Return
True
if audio is playing, otherwise returnFalse
.
-
audio.
stop
()¶ Stops all audio playback.
Classes¶
-
class
audio.
AudioFrame
¶ An
AudioFrame
object is a list of 32 samples each of which is a signed byte (whole number between -128 and 127).It takes just over 4 ms to play a single frame.
Using audio¶
You will need a sound source, as input to the play
function. You can use
the built-in sounds V2 from the microbit
module, microbit.Sound
, or
generate your own, like in examples/waveforms.py
.
Built-in sounds V2¶
The built-in sounds can be called using audio.play(Sound.NAME)
.
Sound.GIGGLE
Sound.HAPPY
Sound.HELLO
Sound.MYSTERIOUS
Sound.SAD
Sound.SLIDE
Sound.SOARING
Sound.SPRING
Sound.TWINKLE
Sound.YAWN
Technical Details¶
Note
You don’t need to understand this section to use the audio
module.
It is just here in case you wanted to know how it works.
The audio
module consumes AudioFrame
samples at 7812.5 Hz, and uses
linear interpolation to output a PWM signal at 32.5 kHz, which gives tolerable
sound quality.
The function play
fully copies all data from each AudioFrame
before it
calls next()
for the next frame, so a sound source can use the same
AudioFrame
repeatedly.
The audio
module has an internal 64 sample buffer from which it reads
samples. When reading reaches the start or the mid-point of the buffer, it
triggers a callback to fetch the next AudioFrame
which is then copied into
the buffer. This means that a sound source has under 4ms to compute the next
AudioFrame
, and for reliable operation needs to take less 2ms (which is
32000 cycles, so should be plenty).
Example¶
from microbit import display, sleep, button_a
import audio
import math
def repeated_frame(frame, count):
for i in range(count):
yield frame
# Press button A to skip to next wave.
def show_wave(name, frame, duration=1500):
display.scroll(name + " wave", wait=False,delay=100)
audio.play(repeated_frame(frame, duration),wait=False)
for i in range(75):
sleep(100)
if button_a.is_pressed():
display.clear()
audio.stop()
break
frame = audio.AudioFrame()
for i in range(len(frame)):
frame[i] = int(math.sin(math.pi*i/16)*124+128.5)
show_wave("Sine", frame)
triangle = audio.AudioFrame()
QUARTER = len(triangle)//4
for i in range(QUARTER):
triangle[i] = i*15
triangle[i+QUARTER] = 248-i*15
triangle[i+QUARTER*2] = 128-i*15
triangle[i+QUARTER*3] = i*15+8
show_wave("Triangle", triangle)
square = audio.AudioFrame()
HALF = len(square)//2
for i in range(HALF):
square[i] = 8
square[i+HALF] = 248
show_wave("Square", square)
sleep(1000)
for i in range(len(frame)):
frame[i] = 252-i*8
show_wave("Sawtooth", frame)
del frame
#Generate a waveform that goes from triangle to square wave, reasonably smoothly.
frames = [ None ] * 32
for i in range(32):
frames[i] = frame = audio.AudioFrame()
for j in range(len(triangle)):
frame[j] = (triangle[j]*(32-i) + square[j]*i)>>5
def repeated_frames(frames, count):
for frame in frames:
for i in range(count):
yield frame
display.scroll("Ascending wave", wait=False)
audio.play(repeated_frames(frames, 60))