The Computer Revolution/Hardware/Refresh Rate vs. Sampling Rate
The refresh rate refers to monitors, televisions and other visual display devices. It is also known as: "vertical refresh rate", or "vertical scan rate for CRTs. It refers to the number of times in a second that a display is fully lit up. For a CRT (Cathode Ray Tube) this is the number of times the ray draws from the top corner of the screen to the opposite bottom corner, in one second. It is measured in hertz. It is this phenomenon that causes the bar on a screen that is seen on a television show as the refresh rate is not enough to compensate for the intermediate frames taken by the camera.
This is in contrast to a frame rate, which is the number of frames shown per second. Whereas if a monitor has a 48Hz refresh rate and the show is at a 24 frame rate, then the screen will be lit up twice for each frame that appears on the screen.
The sampling rate for audio is the equivalent to the refresh rate for video. There are instances that the refresh rate is called the sampling rate interchangeably. In audio, this is the number of times a second that the sound input is recorded and saved. The sample rate of an audio recording is a good indicator of the overall sound quality. With the same measurement unit as the refresh rate, it is a noticeably higher number for a sampling rate for audio. Here are some rates and what they are commonly used for:
- 8,000 Hz - telephone, adequate for human speech
- 11,025 HzC
- 22,050 Hz - radio
- 32,000 Hz - miniDV digital video camcorder, Digital Audio Tape (LP mode)
- 44,100 Hz - audio CD, also most commonly used with MPEG-1 audio (VCD, SVCD, MP3)
- 47,250 Hz - world's first commercial PCM sound recorder by Nippon Columbia (Denon)
- 48,000 Hz - digital sound used for miniDV, digital TV, DVD, Digital Audio Tape, films and professional audio
- 50,000 Hz - first commercial digital audio recorders from the late '70s from 3M and Soundstream
- 50,400 Hz - sampling rate used by the Mitsubishi X-80 digital audio recorder
- 96,000 or 192,000 Hz - DVD-Audio, some LPCM DVD tracks, BD-ROM (Blu-ray Disc) audio tracks, and HD DVD (High-Definition DVD) audio tracks
- 2.8224 MHz - Super Audio CD, 1-bit sigma-delta modulation process known as Direct Stream Digital, co-developed by Sony and Philips