Why Latency Matters: How an Audio Interface can Help
In an audio production environment, latency refers to the time taken for an audio signal to travel through, and be processed by, an audio workflow. Latency matters because when it gets too large it becomes noticeable and hinders the production process. Fortunately, a good audio interface can help to reduce latency.
In this article we’ll look at:
- What is audio latency?
- What causes latency?
- How much latency is too much?
- How audio interfaces can help to reduce latency
What is audio latency?
Think of a typical digital audio production workflow:
- A guitar or voice generates an (analog) sound signal
- The sound signal is converted to an electrical (audio) signal if necessary (via a microphone)
- This signal then travels through cables and into an audio interface
- It gets converted from an analog signal to a digital signal through a process of analog-to-digital conversion (ADC)
- The digital signal flows into a computer system and a digital-audio-workstation (DAW) software package for processing
- The (digital) output of the DAW flows back to the audio interface and gets converted back to an analog signal through a process of digital-to-analog conversion (DAC)
- Finally, the (analog) signal leaves the audio interface and moves to the output system (ie. headphones or amplified speakers)
This whole process takes time. And the time that’s taken, or the delay, for an audio signal to loop through this process is called latency.
Latency matters—when it gets too high, it becomes noticeable—and hinders the audio production process.
Let’s take a closer look at latency.
What causes latency?
Electrical (audio) signal transmission occurs at very fast speeds in modern systems—measured in milliseconds (thousandths of a second)—but the time taken for an audio signal to traverse an audio production workflow still adds up.
The key causes of latency in a digital audio workflow are:
- ADC and DAC processing
- Internal buffering in the audio interface
- The buffer setting in DAW software
- Computer processor speed
ADC and DAC processing is complex and handled by dedicated hardware in audio interfaces.
Both processes need to occur in an audio workflow, ie. analog sound needs to be converted to a digital signal (ADC) for computer processing, and then back again to an analog signal (DAC) for amplification and human hearing.
The ADC and DAC processes together can add 1-2 milliseconds to latency.
Set your buffer size carefully
Buffers are used to store temporary memory in digital systems. In a digital audio workflow, buffers are used during signal transport and also by device drivers in the computer system.
The purpose of buffers is to help ease the burden on a computer’s processor—the higher the buffer, the lower the burden on the processor, and vice-versa.
This is because buffers store data before passing it to the processor, so the more that’s held by the buffer, the more time the processor has to get through its workload.
You can set the buffer size in DAW software packages, typically having a choice between 32, 64, 128, 256, or even 1,024 samples.
There’s a tradeoff, however—the higher your buffer setting, the more latency in your system. And setting your buffer too low may over-tax your processor and lead to distortion or other undesirable effects.
This is where computer processing speed plays a role—the more powerful your computer’s processor, the smaller buffer size you need to use. All else equal, this will result in less latency.
In practice, a fair degree of trial and error is required in setting the right buffer size for your particular setup.
Device drivers can make a big difference to latency
Device drivers are pieces of software that help more complex software programs communicate and interact with pieces of hardware in a digital system.
They are the biggest variable in contributing to latency, adding quite a lot, or not so much, depending on the operating system and software-hardware combination in the system.
Some audio interfaces rely on the computer operating system’s built-in driver, while other interfaces come with custom-built driver software—these usually provide better latency performance.
So, in terms of latency, the drivers that an audio interface uses play an important role—the better (or more customized) the driver, the better the latency outcome usually is.
How much latency is too much?
As we’ve seen, latency is unavoidable in a digital audio production workflow. But how much can we tolerate before it starts to become a problem?
To help answer this question, consider that sound travels at around 340 meters per second.
If you’re sitting around 1 meter away from a piano, say, you’ll hear the piano’s sound after around 3 milliseconds. This delay (latency) is small enough to go unnoticed by human ears.
But what about when the delay gets larger?
According to Presonus, a leading audio equipment manufacturer, if the latency starts to exceed around 12 milliseconds then most listeners will notice it.
At this point, latency can start to become quite distracting and counterproductive for a music production environment.
How audio interfaces can help to reduce latency
As we’ve seen, there are many factors impacting latency in a digital audio system, including the distance to travel through the system, buffering, and ADC/DAC processing, amongst others. All of this will add to latency.
Fortunately, audio interfaces can help to reduce latency. There are three ways in which they do this:
- They are purpose-built hardware and software devices with dedicated drivers
- They come with a variety of connection types
- They offer direct monitoring
Let’s take a closer look.
Latency using a sound card vs an audio interface
So far, we’ve been discussing digital audio workflows that include audio interfaces.
But what if you don’t have an audio interface in your workflow?
In this case, you’ll probably need to rely on your computer system’s in-built sound card for the ADC and DAC processing that’s necessary for digital audio production.
(The “sound card” may simply be a “sound chip” built into the computer’s motherboard—we’ll refer to both possibilities as a sound card.)
But sound cards are not purpose-built for ADC and DAC in the way that audio interfaces are, and they don’t have dedicated drivers.
Hence, sound cards typically result in higher latency than audio interfaces.
The additional latency of sound cards relative to audio interfaces can make a big difference in digital audio workflows.
The latency for a typical headphones output from a sound card, for instance, can be as high as 20 milliseconds. This far exceeds the 12 milliseconds level at which latency becomes noticeable.
By comparison, a good audio interface would have a latency of just a few milliseconds for a similar task.
Most modern audio interfaces come with three ways in which to connect to your computer: USB, Thunderbolt, or PCIe.
Of these, USB is usually the slowest.
PCIe typically comes with high-end professional interfaces and connects directly to a computer’s internal processing, offering the fastest data handling and lowest latency of the three.
Thunderbolt is also very fast as it can employ direct memory access through specially designed drivers, resulting in high data handling efficiency and very low latency.
You can therefore choose the audio interface that best meets your latency needs based on the connection type it offers.
Many audio interfaces allow the audio signal to bypass the computer and DAW software, going straight to the headphone and line outputs instead—a feature called direct monitoring.
With direct monitoring, you can listen to the input signal of an interface with near-zero latency.
There is usually an in-built mixer available on interfaces that offer direct monitoring, allowing you to adjust the balance between your (direct) input signal and the playback from your DAW software.
Direct monitoring offers a convenient way of avoiding the issues of latency during an audio production session.
Latency refers to the time it takes for an audio signal to travel through an audio production system.
It is the delay that you hear between producing a sound (eg. playing a guitar note) and hearing its output from the system (through headphones or amplified speakers).
When latency gets too large, around 12 milliseconds or more, it becomes noticeable. Beyond this point, latency can hinder the audio production process.
Other than the time taken to travel through cables and hardware, however, latency is impacted by ADC and DAC processing, buffering, and computer processing speed.
Fortunately, audio interfaces can help to reduce latency.
They do this by having dedicated hardware (ADC and DAC units) and software (drivers) that are far more efficient than using, say, a computer’s in-built sound card.
They also offer a choice of connection types, so you can choose the type that best meets the latency needs of your system.
What’s more, many audio interfaces offer direct monitoring functionality—this allows near zero-latency monitoring of your input sound. Direct monitoring can be a great way to avoid latency issues in a digital production environment.
So, while latency is unavoidable in a digital audio workflow, audio interfaces can help to reduce and manage it.
You can choose an audio interface that best meets your workflow needs, and adjust your system parameters (such as buffering) to get the best latency outcome for your production process.