Carnegie Mellon

Carnegie Mellon Sound

Carnegie Mellon Sound Sampling Basics Common Sampling Rates 8KHz (Phone) or kHz (Phone, NeXT) kHz (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.

Carnegie Mellon 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!

Carnegie Mellon What’s in a Sound File Format Header Information Magic Cookie Sampling Rate Bits/Sample Channels Byte Order Endian Compression type Data

Carnegie Mellon Example File Format (NIST SPHERE) NIST_1A 1024 sample_rate -i channel_count -i 1 sample_n_bytes -i 2 sample_byte_format -s2 10 sample_sig_bits -i 16 sample_count -i sample_coding -s3 pcm sample_checksum -i end_head

Carnegie Mellon 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 1=mono, 2=stereo 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 0x24 data chunk id 'data' 0x28 length of data chunk (32-bits) 0x2C Sample data

Carnegie Mellon Mu-Law u-LAW (or mu-LAW) is sgn(x) y= ln( 1+ u |x|) ln(1+u) u=100 or 255, A=87.6, mp = Peak message value,

Carnegie Mellon Compression u-LAW sihttp://shuttle.nasa.gov/askmcc/answers/lence 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

Carnegie Mellon 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.

Carnegie Mellon 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 can’t 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 can’t to listen to the higher-quality sample. Check out

Carnegie Mellon Space Requirements Storage Requirements for One Minute of Sound

Carnegie Mellon References (conversion tool) ip

Carnegie Mellon Sound That’s all for today