Theory
In simple terms, latency is the amount of time it takes for a signal to pass from the start of a system to the end. In pro audio terms, it is most commonly known as the time delay between playing a note on a midi controller keyboard, and sound coming out of your monitors, or the time taken between singing a note and hearing it through headphones.
Latency problems can severely affect your projects, so it is important to know how to manage or reduce it. The following factors can affect latency:
- A/D Converter
Whether this is a sound card or external interface, the A/D converter will add some milliseconds to the signal chain. Speed and quality of conversion is key. Interfaces with a super fast rate will not necessarily also have great A/D conversion.
- USB Bus
The signal is then sent through a USB cable. This also adds time….
- Audio Driver (ASIO)
The signal is then accessed by the driver that links your audio software to hardware. ASIO is particularly good because it allows the audio stream to bypass the normal Windows based audio processing kernel (which is comparatively slow).
The process is then reversed to send the signal back to the D/A converter, and we hear sound from our output device. Audio software will typically only measure the latency of the ASIO driver stage, therefore a stated latency time of 2.9ms in reality could be closer to 22ms!
Practice
Many musicians like to adjust the settings of their audio drivers for different situations. For example, when recording, it is useful to have the lowest possible latency by reducing the buffer. When mixing, however, it can be useful to increase the buffer size to allow the software more time to process all data correctly, leading to less stuttering or fewer dropouts.
New Technology
Intel’s new Thunderbolt interfaces were designed to have very low latency, as the specification allows almost direct access to the CPU, reducing latency to as little as 3-6ms. Coupled with a huge data transfer rate, this spec could theoretically offer simultaneous transfer of thousands of channels of high quality audio! Thunderbolt also carries a lot of power, 10W, compared to the 4.5W of USB 3.0, which allows for more powerful pre-amps and hardware. All this doesn’t come cheap however, you can expect to fork out a lot more for a Thunderbolt powered interface!
https://www.studiospares.com/Studio-Gear/Audio-Interfaces/Apogee-Quartet_321070.htm
