Latency is the one big problems that you have when a computer is processing audio, and you're listening back either through headphones or speakers . If there is any delay, our ears will have a tough time syncing the visual and physical parts. Jamulus Servers goes a long way in solving this dilemma.
Latency from a general point of view is the time delay between the visual and audio. Audio Latency refers to a short period of delay (usually measured in milliseconds) between when an audio signal enters a system and emerges.
Latency in live performance occurs naturally from the speed of sound. It takes sound about 3 milliseconds to travel 1 meter (3.28084feet). So 30ft or less is OK and any further and the musicians will not be in-sync.
Latency can be a particular problem when performing on-line using audio platforms on computers. Latency happens when recording or performing a vocal or an instrument. It is the time delay that you hear between the live performance, the processing by a computer or electronic equipment, and the playing back through monitors or headphones .
Latency is measured in milliseconds (ms), which is thousandths of a second. Each 1 milliseconds of latency is roughly equal to 1 foot of distance or 3 milliseconds to travel 1 meter. So 30ms of latency is trying to play an instrument in sync with someone that is 30 feet away.
For performing music on-line with fellow musicians. Anything below < 20ms to 30ms is not very noticeable. The lower, the better. When performing live, latency is never an issue unless you are far away, and the performance is projected in real-time on huge screens. You might then see the image is not synced with the audio as light and sound travel at different speeds.
When using the Jamulus servers and your computer to process the audio both going up and down, that latency adds up. Live the speed of sound that is used to measure the latency. When going on-line, it's the speed of light, so the physically closer you are to the server for to and from the return trip, the better. Within 500 miles is a good gauge. So, jammin' from New York City to Hawaii would be an issue that can not be resolved. See the math below.
- New York City (NYC) to Hawai`i is 8000km
- Speed of Light 299792458 meters per second (approximately 300000 km/s, or 186000 mi/s), The speed of light passing through glass/(fiber) or air is slightly lower. Through wire cables albeit slower as well. But 300000 km/s is approx and good for our measurements.
- So it's 26 milliseconds (ms) one-way to Hawaii from NYC, round trip is 52ms. That will never be any slower. Pretty fast for data and voice phone calls but not for musical performances.
That 52ms is like 52ft or approx 15+ meters. Musicians need 30ft or 9 meters to play together.
What's the Best Number
The lower the milliseconds (ms) the better. Single digits are great and will be like standing a meter apart. Anytime above 40ms and you will notice a difference.
Optimized For Sound Linux Systems
On Linux there are several distributions (distros), that are optimized for making music and support real-time capabilities for music production. These distros include, Ubuntu Studio , KXStudio based off Ubuntu Studio, AV Linux . Here is a page listing maintains and several legacy, unmaintained distros: Linux Audio Bundles and Distributions . These distros typically use the Linux Audio Kernels .
Here is a web page of tips regarding How Audio Latency Can Affect Your Recording and Mixing from Practical Music Production.