Adobe 65009626 User Guide - Page 13

USING SOUNDBOOTH CS4 9 Digital audio fundamentals Sample rate 11,025 Hz 22,050 Hz 32,000 Hz 44,100 Hz 48,000 Hz 96,000 Hz Quality level Poor AM radio (low-end multimedia) Near FM radio (high-end multimedia) Better than FM radio (standard broadcast rate) CD Standard DVD High-end DVD Frequency range 0-5,512 Hz 0-11,025 Hz 0-16,000 Hz 0-22,050 Hz 0-24,000 Hz 0-48,000 Hz Understanding bit depth Bit depth determines dynamic range. When a sound wave is sampled, each sample is assigned the amplitude value closest to the original wave's amplitude. Higher bit depth provides more possible amplitude values, producing greater dynamic range, a lower noise floor, and higher fidelity. For the best audio quality, remain at 32-bit resolution while transforming audio in Soundbooth, and then convert to a lower bit depth for output. Bit depth 8-bit 16-bit 24-bit 32-bit Quality level Telephony CD DVD Best Amplitude values 256 65,536 16,777,216 4,294,967,296 Dynamic range 48 dB 96 dB 144 dB 192 dB 192 dB 144 dB 96 dB 48 dB 0 dB 8-bit 16-bit 24-bit 32-bit Higher bit depths provide greater dynamic range. Audio file contents and size An audio file on your hard drive, such as a WAV file, consists of a small header indicating sample rate and bit depth, and then a long series of numbers, one for each sample. These files can be very large. For example, at 44,100 samples per second and 16 bits per sample, a mono file requires 86 KB per second-about 5 MB per minute. That figure doubles to 10 MB per minute for a stereo file, which has two channels. How Soundbooth digitizes audio When you record audio in Soundbooth, the sound card starts the recording process and specifies what sample rate and bit depth to use. Through Line In or Microphone In ports, the sound card receives analog audio and digitally samples it at the specified rate. Soundbooth stores each sample in sequence until you stop recording. Updated 15 July 2009