CSC231 Lab 6 2010

--D. Thiebaut 13:51, 25 October 2010 (UTC)

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This lab covers sound files in the WAV format, and performing various operations on a sound file using array operations.

The Format of Sound Files

• The document https://ccrma.stanford.edu/courses/422/projects/WaveFormat/ covers the WAV format pretty well, and can be a source of additional information

Part 1

Get the code

• Get a copy of the required files
  • readWaveFileSkel.asm
  • wav.inc

or simply get them with getcopy

 getcopy readWaveFileSkel.asm
 getcopy wav.inc

Get sound files

• Get the sample wav files hello.wav and goodbye.wav as well:

 getcopy hello.wav
 getcopy goodbye.wav

(there's more at http://buggerluggs.tripod.com/ie/wav-dir184.htm )

Play the sound

• Play the files with aplay to make sure you can hear them:

aplay goodbye.wav
Playing WAVE 'goodbye.wav' : Unsigned 8 bit, Rate 8000 Hz, Mono

• Important: make a note of the size of the samples, in this case 8 bits, unsigned.

Assemble, Link and Run

• Do not modify readWavFileSkel.asm yet. On its own it will create a new copy of the goodbye.wav under the name goodbye2.wav.

• Assemble and link the file

nasm  -f elf readWavFileSkel.asm
ld -o readWavFileSkel readWavFileSkel.o
rm goodbye2.wav
./readWavFileSkel

• Check that you now have a new file in your directory called goodbye2.wav

• Play it.

 aplay goodbye2.wav

(Note: on a mac, you can use afplay from the command line instead of aplay.)

You should hear the same thing as you did when listening to the goodbye.wav file.

Part 2

Test #1: Increase intensity

• Make a copy of readWavFileSkel.asm and call it readWavFile1.asm

• Modify it so that you multiply the intensity of the sound by 2.

• Listen to the result. Can you still understand the message?

• Copy goodbye2.wav into goodbye.wav and repeat the process. Still understandable?

Test #2: Decrease Intensity

• Same thing, but this time you will divide the intensity by 2. A good way to divide by two is to shift the binary pattern to the right. For example, to shift right the contents of eax by one bit, do this:

         shr      eax, 1

Test #3: Twice the Sound

• Double up the size of the wav file, making it repeat the sound "goodbye" twice, so that you will hear "goodbye, goodbye".