1. Field of the Invention
The present invention relates to digital audio, and more specifically, to volume control in digital audio systems.
2. Description of the Prior Art
Digital audio systems are typically found in computers and portable electronics. Owing to the fact that digital data allows for easier error detection and data correction, digital audio systems are generally more reliable in reproducing high-fidelity output.
FIG. 1 illustrates a representative analog audio signal 10 along with an 8-bit digital representation 12 at a sample point 14. Typically, the entire audio signal is sampled in this way, however, only one sample point is shown here for clarity. At the sample point 14, the level of the analog audio signal 10 is shown to have a binary value of “10101101” (decimal value “173”), which corresponds to a volume. Such sampling is usually initially performed by a analog-to-digital converter; within the domain of a digital audio system, samples such as the 8-bit digital representation 12 are used.
In the prior art, volume (or level) control can be preformed in the analog or digital domain. In the analog domain, that is, after digital signal processing but prior to speaker output, an operational amplifier having variable input and feedback resistances is usually used. In chip-based applications, these variable resistances are implemented by a resistor tree or the like and an associated multiplexer. As such, volume control in the analog domain can be hardware and time intensive.
Volume control in the digital domain can be accomplished by arithmetic processing of the digital signal (such as signal 12 of FIG. 1). Such processing can be accomplished by a multiplier for multiplying the signal by level factors stored and selected from a read-only memory (ROM). This is a flexible approach since the resolution of volume control depends mainly on the size of the ROM. However, this is also a hardware and time demanding method.
Improvements in audio schemes (e.g. Intels Azalia) place constant demand on the industry to improve and create new methods of signal processing. As such, there is a need for an improved method of digital audio volume control, and specifically, one which reduces hardware complexity while improving performance.