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Computer audio is one of the most overlooked aspects of a computer purchase. With little information from the manufacturers, users have a hard time figuring out exactly what it is they are getting. In the first segment of this series of articles on Understanding Computer Audio, we look at the basics of digital audio and the specifications may be listed. In addition, we will look at a couple of the standards that are used to describe the components.
All audio that is recorded or played through a computer system is digital, but all audio that is played out of a speaker system is analog. The difference between these two forms of recording play an important role in determining the ability of sound processors.
Analog audio uses a variable scale of information to try and best reproduce the original sound waves from the source. This can produce a very accurate recording, but these recording degrade between connections and generations of recordings. Digital recording takes samples of the sound waves and records it as a series of bits (ones and zeros) that best approximate the wave pattern. This means that the quality of the digital recording will vary based on the bits and samples used for the recording, but the quality loss is much lower between equipment and recording generations.
When looking at sound processors and even digital recordings, the terms of bits and KHz will often come up. These two terms refer to the sample rate and audio definition that a digital recording can have. There are three primary standards used for commercial digital audio: 16-bit 44KHz for CD Audio, 16-bit 96KHz for DVD and 24-bit 192KHz for DVD-Audio.
The bit-rate refers to the number of bits used in the recording to determine the amplitude of the sound wave at each sample. Thus, a 16-bit bit-rate would allow for a range of 65,536 levels while a 24-bit allows for 16.7 million. The sample rate determines the number of points along the sound wave that are sampled over a period of one second. The greater the number of samples, the closer the digital representation will be to the analog sound wave.
With this general understanding, what exactly should one look for when examining the specifications for an audio processor? In general, it is best to look for one capable of 16-bit 96KHz sample rates. This is the level of audio used for the 5.1 surround sound channels on DVD movies. For those looking for the best audio definition, the new 24-bit 192KHz solutions are better.
Another aspect of audio components that users will come across is a Signal-to-Noise Ratio (SNR). This is a number represented by decibels (dB) to describe the ratio of an audio signal compared to the noise levels generated by the audio component. The higher the Signal-To-Noise ratio, the better the sound quality is. The average person generally cannot distinguish this noise if the SNR is greater than 90dB.
When reading the audio specifications, called AC'97 Compatible audio often comes up. This is a specification developed by Intel for audio processors integrated on computer motherboards. All AC'97 audio solutions support the 16-bit 96KHz, 6-channel playback for DVD surround sound recordings. This specification does not guarantee quality levels, so solutions may have various Signal-to-Noise Ratios. The specification also does not detail what surround sound modes are supported.
Another standard that might be referred to is 16-bit Sound Blaster compatible. Sound Blaster is a brand of audio cards created by Creative Labs. The Sound Blaster 16 was one of the first major sound cards to support the 16-bit 44KHz sampling rate for CD-Audio quality computer audio. This standard is below that of the newer AC'97 standard and will only be found on older computers. For those only worried about CD quality audio and not intending to use surround sound or DVD movies, this may be sufficient for them.
EAX or Environmental Audio Extensions is another standard that was developed by Creative Labs. Instead of a specific format for audio, it is a set of software extensions that modify audio to replicate the effects of specific environments. For example, the audio being played in a computer could be designed to sound as if it was being played in a cave with lots of echo. Support for this can exist in either software or hardware. If rendered in hardware, it uses fewer cycles from the CPU. There are currently three versions: EAX, EAX2 and EAX3.
Finally, some products may carry the THX logo. This is essentially a certification that THX Laboratories feels that the product meets or exceeds their minimum specifications. Just remember that a THX certified product will not necessarily have better performance or sound quality than one that does not. The manufacturers have to pay THX labs for the certification process.
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