undefined local variable or method `raw_audio' for main:Object (NameError)

[tablecell]

test.rb

require 'opus-ruby'

# Create new encoder with a sample rate of 48 kHz, a frame size of 480 bytes and 1 channel
encoder = Opus::Encoder.new 48000, 480, 1
# Set the bitrate to 32 kbit/s
encoder.bitrate = 32000
# Set the VBR rate to 0 (CBR)
encoder.vbr_rate = 0

# Encode some raw audio
encoded = encoder.encode(raw_audio, 960)

# Safely destroy encoder
encoder.destroy

ruby test.rb
in <main>': undefined local variable or methodraw_audio' for main:Object (NameError)

I want record audio from system audio device