We are using mobile phones and many digital audio devices and the audio signals are digitized and converted to analog signals that we can hear and enjoy.
A very important technology that is used behind reproducing the best sounds is the concept of pre-emphasis and de-emphasis.
A very important technology that is used behind reproducing the best sounds is the concept of pre-emphasis and de-emphasis.
In processing electronic audio signals, pre-emphasis refers to a system process designed to increase (within a frequency band) the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena asattenuation distortion or saturation of recording media in subsequent parts of the system. That is the mirror of the deemphasis. The whole system is called emphasis. The frequency curve is decided by special time constants. The cutoff frequency can be calculated from that value.
Pre-emphasis is commonly used in telecommunications, digital audio recording, record cutting, in FM broadcasting transmissions, and in displaying the spectrograms of speech signals.
An example of this is the RIAA equalization curve on 33 rpm and 45 rpm vinyl records.
In high speed digital transmission, pre-emphasis is used to improve signal quality at the output of a data transmission. In transmitting signals at high data rates, the transmission medium may introduce distortions, so pre-emphasis is used to distort the transmitted signal to correct for this distortion. When done properly this produces a received signal which more closely resembles the original or desired signal, allowing the use of higher frequencies or producing fewer bit errors.
In telecommunication, de-emphasis is the complement of pre-emphasis, in the antinoise system called emphasis. Emphasis is a system process designed to decrease, (within a band of frequencies), the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation differences or saturation of recording media in subsequent parts of the system.
Special time constants dictate the frequency response curve, from which one can calculate the cutoff frequency.
Pre-emphasis is commonly used in audio digital recording, record cutting and FM radio transmission.
In serial data transmission, de-emphasis has a different meaning, which is to reduce the level of all bits except the first one after a transition. That causes the high frequency content due to the transition to be emphasized compared to the low frequency content which is de-emphasized. This is a form of transmitter equalization; it compensates for losses over the channel which are larger at higher frequencies. Well known serial data standards such as PCI Express, SATA and SAS require transmitted signals to use de-emphasis.