Fixing Audio Latency Part 1
Latency - what it is and why you don't want it. Ian Waugh gives the low down on the slow down...
Latency is a delay. It's most evident and problematic in computer-based music audio systems where it manifests as the delay between triggering a signal and hearing it. For example, pressing a key on your MIDI keyboard and hearing the sound play through your sound card.
It's like a delayed reaction and if the delay is very large it becomes impossible to play anything in time because the sound you hear is always a little bit behind what you're playing which is very distracting.
This delay does not have to be very large before it causes problems. Many people can work with a latency of about 40ms even though the delay is noticeable, although if you are playing pyrotechnic music lines it may be too long.
The ideal latency is 0 but many people would be hard pushed to notice delays of less than 8-10ms and many people can work quite happily with a 20ms latency.
The trouble with latency is not just the delay you get when playing a keyboard but the problem caused when trying to record a new track while listening to previously-recorded tracks. Most people like to listen to (i.e. monitor) pre-recorded tracks while laying down a new one and this is where the problem appears. Even a small delay will cause you to play the new track out of sync so the timing will be out between the tracks.
Incidentally, there is not usually a latency problem playing recorded tracks as most sequencers compensate for any latency in the system to ensure that playback is perfectly in sync.
The hard and the soft of it
Latency is caused by a combination of the hardware (the sound card) and the drivers. Some sound cards, particularly those specifically designed for music use, have a very low latency. Others, such as consumer sound cards, may not give the matter much consideration.
It is, however, well worth visiting your sound card manufacturer's site to check for new drivers which may reduce latency.
Windows has its own audio drivers called MME (for Multi Media Extension). These are general purpose drivers and will usually give the worst latency settings for music, which could be as high as 750ms.
Easy come easy go with ASIO
Most cards with half an interest in the music market have ASIO drivers. This stands for Audio Stream Input/Output (not a lot of people know that!) and the system was developed by Steinberg (developer of the Cubase sequencing software) to improve latency in sound cards.
Any sound card hoping to catch the ear of the musician will have an ASIO driver so that's the first good gauge of its suitability for music.
In 1999 Steinberg introduced the ASIO 2 standard which includes other features useful to the musician. These include Direct Monitoring which routes the incoming signal directly back through the sound card's output, thus bypassing the internal audio system completely. However, do note that both the hardware and the driver must support Direct Monitoring in order for this to work and not all ASIO 2 systems do.
In the second part of this feature we look at ways to work around the latency problem if you have a system with high latency, and check out the latency in the popular SoundBlaster sound cards.