21st Century music stands use real-time Windows software for a perfect mix.

Real-time mixing and monitoring is a key requirement for members of a band or orchestra that want to hear themselves playing during rehearsals. Musicians that can’t hear themselves clearly will not produce the same quality sound as those who can. Enabling each player to set the sound levels that only he or she hears (through headphones) makes a stage less noisy and improves the quality of the sound that the audience hears. SamePage Mix application software by Corevalus Systems of Georgetown Kentucky allows a musician to set sound levels for up to 16 different audio channels and save the level settings for each piece on a playlist, to be retrieved later during a musical performance.

What makes SamePage Mix unique in the music industry is that it combines the function of a personal mixing station with that of an on-line electronic music stand on an affordable Windows PC platform. Windows alone however, doesn’t guarantee determinism in processing real-time tasks, and if the music isn’t processed in real-time, the quality of the sound produced will suffer. “The problem with Windows is that it likes to take control,” said Mark Craig, Vice President of Corevalus Systems. “But we need to listen to 16 channels over the network, do mixing and output through the audio card in under 5 milliseconds. Windows by itself can’t handle that reliably.”

Corevalus’ engineers found that if it takes more than 5 milliseconds for the sound to go from a guitar through some headphones to the guitar player’s ear, the player will perceive that his or her monitor is not correctly following the sound. Hence systems with this much delay can’t be used successfully as live mixing stations. Without an operating system that is capable of deterministic processing of I/O, it’s impossible to predict exactly when a computer will respond to its inputs – no matter how fast the computer’s processor.

The Corevalus engineers looked for a real-time operating system (RTOS) that would handle the time-dependent processing and also run along side Windows applications on the same Windows platform. Their search led them to INtime for Windows from TenAsys Corp. of Beaverton, Oregon. “The fact that INtime was designed to work along with Windows was key,” said Mark. “All of our human interface and mixing code was written for Microsoft’s Windows-based Visual Basic and we didn’t want to re-write everything in order to add the real-time element.”

Corevalus’ software runs on a 19-inch touch screen PC-compatible computer (Figure 1), which early versions of the company’s software used simply as a digital music stand. As the software evolved and expanded, and the mixing function was added to the company’s software offering, the processor was updated to a dual-core Intel Mini-ITX Atom motherboard.

Corevalus’ SamePage Mix software is divided into two subsystems, each running on its own core of a dual-core Intel processor (See Figure 2). TenAsys’ INtime leverages the Intel processor’s on-chip hardware support for virtualization to set up virtual machine environments for both the real-time and Windows subsystems, with the real-time software given exclusive control of time-critical I/O. This ensures that Windows tasks cannot interrupt the real-time I/O processing. INtime controls the entire network side of the application, where the software listens to the traffic on the 100 base-T Ethernet network, and separates the non-audio information from the 16 channels of audio. The network also handles non-audio information including musical scores, which are stored in the Internet cloud.

INtime real-time application software also does some equalization on each individual channel before passing the finished product to a PC-based sound card for creating the sound for the musician. When the real-time and Windows-based software subsystems communicate, they do so via shared memory.

Due to INtime for Windows’ optimization for minimum latency in responding to I/O, all the sound processing, level adjustment and equalization, and outputting to the listener happen with only 3 milliseconds of latency, short enough to beat the 5 millisecond goal with some time to spare.

One of the most attractive features of the system is the fact that it is based on high volume PC technology. This is in contrast to systems developed specifically for the pro audio world, which are produced in low volumes and are therefore expensive.

The concept of using a PC touchscreen device to emulate traditional live sound mixing stations is a relatively new concept in high-end audio applications. With programmable on-screen sliders and knobs, the system can be set up to do things that wouldn’t be possible with old-fashioned physical controls, for example associating a mix preset with a particular song, which can be automatically retrieved from storage wherever the system operator wants. Now, when a musician goes to perform, he/she doesn’t need to physically set up the mix. During a performance, the sliders can be moved between songs – or even during a song - with the touch of a single button on screen. Also, by making the settings electronic, they can be tweaked remotely by a sound engineer for troubleshooting rather than requiring changes to be made at the musician’s station. This is a unique capability of Corevalus’ Mix software.

Because the INtime for Windows real-time solution can run on processors with different numbers of cores, even single-core processors, Corevalus can offer solutions to its customers at different price points. “By using multi-core Intel processors and embedded virtualization strategies, we can deliver a platform that can scale across different platforms to satisfy customer needs for mixing capability as well as the other features of the digital music stand,” says Mark Craig. “Plus, we have headroom to add new capabilities to our products in the future.”


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