We are starting set of articles about interesting technology areas and solutions we have implemented or encountered in our projects.
This article briefly describes our experience in development of audio device driver and Dolby Pro Logic IIx implementation.
We have developed solution for providing virtual surround for headsets (that have only 2 audio channels) for PC platform. Currently solution supports Windows XP, Windows Vista, Windows 7, 8 and 8.1.
Solution includes kernel mode audio filter driver and user space application that is used for changing various parameters at run-time.
Audio driver is compatible with all kind of applications and has a number of techniques and DSP effects implemented in it:
- Exposing more channels and more speaker configurations than is supported by hardware;
- Downmixing multi-channel streams to streams that contain so many channels as supported by hardware;
- Providing virtual surround using Dolby Headphone and Dolby Pro Logic IIx technologies;
- Fully configurable equalizer with variable range and bands number;
- All parameters are configurable from user space;
- Driver uses kernel-to-user space techniques to notify client programs running in user space about different events, like changes in audio stream.
Technologies used: C++, Windows DDK, Equalizer, Virtual Surround, Dolby.
- After development was completed we needed to pass WHQL audio device qualification and especially Dolby certification, which was interesting part of a project delivery.
Digital signal processing (DSP) effects
Digital signal processing (DSP) is the mathematical manipulation of an information signal to modify or improve it in some way. It is characterized by the representation of discrete time, discrete frequency, or other discrete domain signals by a sequence of numbers or symbols and the processing of these signals.
Digital Signal Processing (DSP) effects process the audio signal. A classic example of an effect is a Graphic Equalizer, which will boost certain frequencies.
Dolby Pro Logic and Dolby Surround
Dolby Pro Logic is a surround sound processing technology developed by Dolby Laboratories, designed to decode soundtracks encoded with Dolby Surround.
Dolby Surround was the earliest consumer version of Dolby’s multichannel analog film sound decoding format Dolby Stereo.
Dolby Stereo, is Dolby Laboratories’ trademark for its various analog stereo cinema sound formats.
A newer Dolby Pro Logic IIx system is also now available, which can take two-channel stereo, Dolby Surround (sometimes called Dolby Stereo Surround) and Dolby Digital 5.1 source material and up-convert it to 6.1 or 7.1 channel surround sound.