Computer Audio Basics: Standards and Digital Audio

Computer audio is one of the most overlooked aspects of a computer purchase. With little manufacturer information, most people have difficulty determining exactly what they are getting.

Digital Audio

All audio recorded or played through a computer system is digital, but all audio played out of a speaker system is analog. The difference between these two recording forms plays an important role in determining the ability of sound processors.

Analog audio uses a variable scale of information to reproduce the original sound waves from the source. This process results in accurate recordings, but these recordings degrade between connections and generations of recordings.

Digital recording takes samples of the sound waves and records them as a series of bits (ones and zeros) that best approximate the wave pattern. The quality of the digital recording varies based on the bits and samples used, but the quality loss is much lower between the equipment and recording generations.

Bits and Samples

The bit depth refers to the number of bits in the recording that determines the amplitude of the sound wave at each sample. Thus, a 16-bit bitrate allows 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.

The sample rate is different than a bitrate. Bitrate refers to the overall data processed in the file per second. Multiply the number of bits by the sample rate, then convert to bytes on a per-channel basis. Mathematically: (bits * sample rate * channels) / 8. So, CD-audio, which is stereo or two-channel, would be:

• (16 bits * 44000 per second * 2) / 8 = 192000 bps per channel or 192 kbps bitrate

Look for bit depth capable of 16-bit 96 kHz sample rates. This is the level of audio used for the 5.1 surround sound channels on DVD and Blu-ray movies. 24-bit 192 kHz solutions offer greater audio quality for those looking for the best audio definition.

Signal-to-Noise Ratio

Another aspect of audio components is a signal-to-noise ratio. This number, represented by decibels, describes the ratio of an audio signal compared to the noise levels generated by the audio component. The higher the SNR, the better the sound quality. The average person generally cannot distinguish this noise if the SNR is greater than 90 dB.

Standards

The AC97 audio standard developed by Intel served as an early framework; it offered support for 16-bit 96 kHz audio for six channels necessary for DVD 5.1 audio sound compatibility. Since then, new advances in audio emerged with high-definition video formats such as Blu-ray.

To support these new formats, a newer Intel High Definition Audio (IHDA) standard expands audio support for up to eight channels of 30-bit 192 kHz, which is necessary for 7.1 audio support. Most AMD hardware labeled as 7.1 audio support can achieve these same levels.

Some products may carry the THX logo. This mark certifies that THX laboratories think the product meets or exceeds its minimum specifications. A THX-certified product will not necessarily have better performance or sound quality than one that does not. The manufacturers pay THX laboratories for the certification process.