Zero Latency Monitoring
How to achieve zero latency monitoring in a digital audio workstation when overdubbing ... without using an expensive audio interface.
My initial disappointment with digital audio came immediately, when I first record-enabled a track. Everything seemed right. The MOTU 2408 audio interface was functioning properly, the mic was live, but for every sound made with my instrument there returned an echo through the monitor (headphones in this particular case).
Musical timing is of the utmost importance to me, and the echo made accurate overdubbing impossible. Attempts to play along with the software metronome were equally frustrating.
The situation was quite disturbing. I thought I was using the 2408 hardware incorrectly; but no hardware solution existed for that device.
This infamous delay/echo issue is called latency—monitor latency to be precise. It confuses and frustrates most people when they first set up in their home recording studios. Click this link to see how how often zero-latency monitoring is discussed.
Understanding and eliminating latency
In this section we'll look at the nature of latency, what causes it, and various methods for eliminating it. In general we'll explore inexpensive solutions that only require:
- some specific hardware wiring
- muted output on any record-enabled tracks in your multi-track audio software
If you want to jump ahead to the three solutions, they are here: a, b, c
The latency loop
Monitor latency occurs when an audio signal runs through the computer and back to you. That trip takes time. If it takes more than 30 or 40 milliseconds, you will hear two separate sounds:
a) the sound you make
b) the return of the sound you made
Latency solutions
There are a number of a solutions to monitor latency, all of which require monitoring "direct" at the interface or "monitoring at the mixer"— in essence this means, "sending the input signal directly to the headphones AND not listening to it through the recording software.
I will illustrate the topic of "monitoring at the mixer" here in great detail. It's relatively simple to create a manageable setup, depending on your needs. I provide a few diagrams for various scenarios below.
NOTE: It's important to understand that any electronic circuit will have some amount of latency.
The result we're looking for is not actually zero-latency, but low-latency. Low-latency is considered to be a delay that's below the threshold of human perception. Audio mixers usually have a 4 to 6 ms latency, but this is not temporally perceptible, but there may be some phase shift coloring to the tone of the sounds (this occurs in monitoring, and is not relayed to the recording.
Here's solution B, the simplest setup, which I will return to in greater detail.
Monitoring "at the mixer"
When monitoring overdubs even minor latency becomes painfully apparent when it enters the threshold of perception. Latency is a problem when trying to play along with a metronome or drum "click-track" within the audio software.)
When I first encountered latency I thought I would find a setting that would entirely alleviate the latency. Not so. My very expensive MOTU 2408 audio interface was unable to eliminate latency because (as an early generation audio interface, and like many of its audio interface peers) it did not have hardware patch through—i.e. no built-in mixer.
The solution was monitoring at the mixer. This allowed me to quickly and comfortably finish my initial project. However, I'll begrudgingly say, I never expected that I would need a mixer to comfortably overdub; relying on a mixer complicates my setup and makes it less portable. But it works, with a few cables you'll be able to duplicate one of the scenarios illustrated here.
Joining the crowd
In my search for a solution to monitor latency I discovered that there were lots of people struggling to resolve or work around audio software latency:
- they were attempting solve the problem using futile (vendor recommended) software settings
- many veered close to a solution but remained off track because they were unclear on one or more key contribution factors (primarily that at various points in the chain, there are places where the signals meet simultaneously, and these are the places where you can monitor without latency).
- many merely tried to adapt their playing, in other words, they tried to synchronize by playing ahead of the audio they were trying to overdub to. This is exactly what I was unwilling to do, because it is utterly distracting and it interfere with the artistic process, which for me it largely about timing. That would be like listening to someone misspell words in my ear while I'm trying to recite poetry.
- understandably some people simply gave up, or resorted to buying an expensive audio interface. I'm not against purchasing equipment, but I think anyone should be able to record with low cost equipment, or whatever is on hand.
What's an acceptable level of latency?
The Hass Effect states that:
- if two sounds occur within 30 to 40ms the listener will not hear two distinct sounds. This suggests that the nervous system has a "frame rate" and when sounds occur within 30 to 40ms, it packages them into a single perceived sound.
- the perceived sound may be colored by a slight phase shift
- the acoustic timber of first sound will dominate the tonal "color" ... so you mainly hear the first sound and some shadow or tail of the second.
In my personal experience all of these Hass Effect premises are true. And I've witnessed countless people perceive these effects.
Specs and buffers
Vendors of digital audio software and hardware tout "low latency", promising delays as low as 12 milliseconds, achieved by lowering the audio buffers in the audio software, and that this can be WITHOUT using a mixer!
The promise of sub 12 millisecond latency is exciting. An analog mixer has a latency of 3 to 5ms, and that's never bothered me! So, if we accept the Hass Effect premise, 12ms latency should be more than acceptable. But my experience with low latency promises consistently contradicts industry claims of 12ms latency.
At best, by lowering buffers, I hear latency in the 100ms range, which is a whopping tenth of a second! Unfortunately lowing the buffers may cause the unpleasant side effect of dropping samples during playback. So in my experience, buffer twiddling fails to actually adequately address the initial problem of latency, and it may cause the side effect of dropped samples. Not a win-win situation.
More realistically manufacturers now hawk their hardware latency solutions. (Um, because software solutions don't really work?) The new professional interfaces indeed offer low latency simply because they include a built-in mixer, thereby allowing you to monitor "at the mixer" within the audio interface. Additionally these mixers usually have access to onboard effects software that allows you to insert effects like reverb, thus providing an excellent monitoring environment for overdubbing. But at a price, usually from $500 to $1000+.
Resolving monitor latency
But what if you want to record and overdub with whatever equipment is available? It is possible to eliminate latency with any setup, without spending big $$$ to create a working home studio. And that's what the remainder of this article is about.
To resolve latency all you really need is:
- an audio interface with a line out (most any audio interface in the $100 range will have XLR mic inputs, line level inputs, a headphone jack, and a USB or FireWire connection
- the addition of a simple mixer provides other options as well
For a software standpoint, the real key is muting the record enabled track, so it is not sent to you monitor outputs, like Built-in Output 1-2. This is how you eliminate the foldback of the live input, the source of the latency.
NOTE: My diagrams refer to Digital Performer (by MOTU). This is one of the top multi-track digital audio applications for recording, editing, and mixing audio. But anywhere I say Digital Performer, the same logic applies if you are using any top tier DAW (digital audio workstation) application, such as:
- Pro Tools (by Avid)
- Logic, and GarageBand, its surprisingly powerful little sibling (by Apple)
- Cubase
- NOTE: It's exciting to know that BIAS (maker of Peak) is releasing an multi-track application in Q2 2011
That's all for now, though I plan to write more on the pros and cons of the various solutions I've diagramed below.
