DARPA Compare

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Sound
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Sound Sampling Basics

• Common Sampling Rates
• 8KHz (Phone) or 8.012820513kHz (Phone, NeXT)
• 11.025kHz (1/4 CD std)
• 16kHz (G.722 std)
• 22.05kHz (1/2 CD std)
• 44.1kHz (CD, DAT)
• 48kHz (DAT)
• Bits per Sample
• 8 or 16
• Number of Channels
• mono/stereo/quad/ etc.

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Common Sound File Formats

• Mulaw (Sun, NeXT) .au
• RIFF Wave (MS WAV) .wav
• MPEG Audio Layer (MPEG) .mp2 .mp3
• AIFC (Apple, SGI) .aiff .aif
• HCOM (Mac) .hcom
• SND (Sun, NeXT) .snd
• VOC (Soundblaster card proprietary standard) .voc
• AND MANY OTHERS!

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Whats in a Sound File Format

• Header Information
• Magic Cookie
• Sampling Rate
• Bits/Sample
• Channels
• Byte Order
• Endian
• Compression type
• Data

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Example File Format (NIST SPHERE)
NIST_1A 1024 sample_rate -i 16000 channel_count
-i 1 sample_n_bytes -i 2 sample_byte_format -s2
10 sample_sig_bits -i 16 sample_count -i
594400 sample_coding -s3 pcm sample_checksum -i
20129 end_head
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WAVe file format (Microsoft) RIFF

• A collection of data chunks.
• Each chunk has a 32-bit Id
• followed by a 32-bit chunk length
• followed by the chunk data.
• 0x00 chunk id 'RIFF'
• 0x04 chunk size (32-bits)
• 0x08 wave chunk id 'WAVE'
• 0x0C format chunk id 'fmt '
• 0x10 format chunk size (32-bits)
• 0x14 format tag (currently pcm)
• 0x16 number of channels 1mono,
  2stereo
• 0x18 sample rate in hz
• 0x1C average bytes per second
• 0x20 number of bytes per sample
• 1 8-bit mono
• 2 8-bit stereo or
• 16-bit mono
• 4 16-bit stereo
• 0x22 number of bits in a sample

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Mu-Law
u-LAW (or mu-LAW) is sgn(x)
y -------- ln( 1 u x)
ln(1u) u100 or 255, A87.6, mp Peak message
value,
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Compression
u-LAW sihttp//shuttle.nasa.gov/askmcc/answers/len
ce detection ADPCM (adaptive, delta PCM, 24/32/40
kbps) LPC-10E (Linear Predictive Coding
2.4kb/s) CELP 4.8Kb/s - builds on LPC GSM
(European Cell Phones, RPE-LPC) 1650 bytes/sec
(at 8000 samples/sec) RealAudio (builds on CELP,
GSM, proprietary) MPEG Audio Layers (builds on
ADPCM) Layer-2 From 32 kbps to 384 kbps -
target bit rate of 128 kbps Layer-3 From 32
kbps to 320 kbps - target bit rate of 64
kbps Complex compression, using perceptual models

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Sound Editing

• GoldWave -
• requires a sound card.
• digital audio sound player, recorder and editor
• can load, play and edit many different file
  formats
• .wav, .au, .voc, .snd
• displays separate graphics for the left and right
  channels
• very easy to use
• good sound quality
• Others WHAM, Cool Edit, SOX, WINPLANY, Digital
  Audio Playback Facility, MOD4Win, etc.

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Tips for Audio on the Web

• There is no generic audio standard on the Web
• Few systems on the Web have 16-bit sound
  capabilities
• Listening to 16-bit sounds on an 8-bit system
  results in strange effects
• Users will be annoyed if they spend a lot of time
  downloading a sound and they cant play it
• Distribute only 8-bit sounds on your Web page
• Or, provide different sound files in both 8-
  and 16-bits
• Record in the highest sampling rate and size you
  can, and then process down to 8-bit
• Keep file size small
• downsampling to 8-bit
• use a lower sampling rate
• use mono sounds
• Describe what format those sounds are in
• WAVE, AIFF, or other format
• Providing the file size in the description is a
  politeness to help estimate download times
• If you need high sound quality and have large
  audio files
• Use a smaller sound clip in m-law format as a
  preview
• or for those who cant to listen to the
  higher-quality sample.

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Space Requirements
Storage Requirements for One Minute of Sound
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References

• http//www.nlc-bnc.ca/pubs/netnotes/notes24.htm
• http//www.spies.com/sox (conversion tool)
• http//freebsd.cdrom.com/.5/cica/sounds/gldwav21.z
  ip

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Sound Thats all for today