MQA Labs Inspira and Endura fix one of the oldest problems in digital audio conversionInspira: $249
Endura: $349
mqalabs.com
When zooming in on the start of a waveform in your DAW, have you ever noticed that the initial transient of the recording is preceded by a wobble of waveform activity? It almost looks like the waveform is revving-up for the big jump of the transient. This strange signal is extremely low in level, so most of us ignore it, but if you were to stick a mic in front of a drum and feed its signal to an old-school analogue oscilloscope, you’d see nothing of the sort, but just a clean, crisp transient.

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So what’s up with those DAW waveforms? Are they actually a bigger problem than we realise? With the release of the Inspira and Endura plugins, MQA Labs certainly thinks so.
Endura. Image: Press
What is pre-ring, and why does it matter?
What you’re seeing is known as time smear or pre-ring; an artefact of the delta-sigma oversampling design used in (practically) every audio analogue-to-digital (AD) converter that’s ever been on the market. If you’d like to understand why pre-ring occurs, check out MQA Labs’ white paper on the topic, but be warned — it gets rather technical!
Pre-ring doesn’t only affect the first transient in a recording, but is an ever-present pre-echo of the upcoming audio. With extremely low amplitude and an extremely short time offset (around 150µs at 48 kHz), you may assume it has no discernible impact. But overlaying audio with a time-offset copy of itself results in phase interactions that amplify some frequencies while attenuating others, and pre-ring causes this to happen.
The actual sonic impact is exceptionally small, but if you know what to listen for (and are able to compare to an analogue source with no pre-ring) it can be heard as a slight over-emphasis of the mid range and coinciding muddying of upper-mid and high frequencies. It can also blur the apparent position of individual sounds within stereo sources.
Inspira. Image: Press
What are Inspira and Endura?
So, where do MQA Labs Inspira and Endura fit into this picture? The company’s goal is to improve conversion technology, and it has developed systems that eliminate pre-ring by preserving the time-domain accuracy lost in delta-sigma converters. Inspira and Endura harness this technology in a way that brings its benefits directly into your DAW, and that works no matter what converters your audio interface employs.
The plugins look incredibly similar (although not identical) to each other, but are intended for different purposes. Inspira is for use on individual parts and tracks, although can be used on submix and mix buses too, if desired. Endura, on the other hand, is only for the master mix bus, where it should be applied as the last processor in the chain after the master fader (although not all DAWs allow inserts following the master fader).
Looked at another way, Inspira deals with pre-ring stemming from the analogue-to-digital (AD) side of things, while Endura applies processing that mitigates pre-ring in the DA conversion process.

What do the plugins do?
The first stage of both plugins shows a single Align control and a graphical representation of an impulse waveform. When the Align dial is in the zero position, no alignment processing is applied, and the graphic shows both pre- and post-ring surrounding the impulse (post-ring equates to decay and reverberation in real-world acoustics and so is considered a natural part of the sound – i.e., we can ignore it). Increasing the Align value shifts the pre-ring forward into the post-ring area; decreasing the value does the opposite.
This pre-ring shift is reflected in the graphic, but this is only an indicator and not something that’s actually being measured from the audio passing through the plugin. Achieving the best Align setting, then, means listening closely to the results… and I mean very closely! I’ve already mentioned that the sonic impact of pre-ring is subtle, and so it follows that the impact of the corrective processing is equally subtle. Accordingly, this makes finding the sweet spot, where the mids are least plummy, and the upper ranges are spacious and detailed, tricky. If it’s possible, MQA should add a real-time pre-ring visualiser.
The second stage of both plugins is dedicated to dithering. Dithering adds a low-level random noise that eliminates the ugly distortion caused by digital quantisation errors. It’s an important stage in any digital signal processin,g but we normally only pay attention to it at output — for example, when your pristine 24-bit mix may be heading for a 16-bit playback format. Having control over dithering in Inspira – essentially the input stage – is therefore unusual but helpful. Still, I find what makes this particularly useful is that it allows control over noise shaping, a key part of both plugins’ dithering stages.
Noise shaping is an EQ curve applied to dithering noise to move the dithering energy away from the frequencies at which our hearing is most sensitive, thus giving the perception of improved sonic detail around those frequencies. Inspira’s dithering, then, is more about using noise shaping to focus accuracy and detail than it is about reducing bit depth. It can have an impact even when the dithering Depth control (expressed in terms of the number of bits being effectively removed) is at zero, while increasing the Depth value (removing bits, in effect) imparts a form of dynamic compression that can be useful too.
Each plugin offers a slightly different choice of six noise shaping curves. Inspira has a flat curve, three Air curves that lift high-end detail, and two Psy curves designed to focus detail where the human ear is most sensitive. Endura trades one of the Air curves for an extra Psy curve, and also has a Learn function that measures the noise floor of a mix from which to produce an appropriate curve. These options are accompanied by a visual readout that overlays the chosen noise shape on a real-time frequency analysis.
Endura Export and Verify view. Image: Press
What on earth is Assurance Metadata?
One of the reasons Endura needs to be placed at the very end of the mix chain is to ensure the proprietary Assurance Metadata generated by the plugin isn’t corrupted by further signal processing. This is data encoded into the audio stream, its primary function being to verify the exported audio is a bit-perfect match to what the DAW is producing.
The metadata is inaudible, and the export/mixdown procedure of most DAWs will leave it intact; if the metadata is corrupted, it means the exported file will not be bit-perfect. Endura can check the metadata and, if it turns out your DAW is not creating a bit-perfect export, you can use the plugin’s built-in export functionality instead.
MQA Labs’ QRONO d2A converters also respond to the metadata, applying specific filtering tailored to settings applied in Endura. This means QRONO-equipped playback systems, which are already gaining a reputation for delivering excellent results, can do an even better job of turning the digital audio data stream back into accurate, realistic, analogue audio.

Do I really need these plugins?
As I’ve mentioned, the impact of Inspira is subtle, but its benefits have a cumulative effect. Mixes take on an analogue-like quality, with the airiness and high-end detail associated with classic recordings from the pinnacle of the analogue era. However, while not a bank-breaker, Inspira isn’t the cheapest of plugins, so it’s perhaps something that will be of most interest to pros, although anyone’s mixes will benefit from it.
Adding Endura to the brew ensures Inspira’s analogue-like detail and naturalness remain locked into final mixes and masters, but it’s aimed primarily at mastering engineers and studios, with a steeper price tag to match.
It’s undeniable that the sonic benefits wrought by these plugins are delicate, but if we sound engineers and producers were unconcerned with audio quality, we’d still be clustering musicians around a ribbon mic connected directly to a wax master cutter!
Key features

VST3, AU and AAX plugins
Compatible with macOS 10.13+ (Intel or Apple Silicon) and Windows 10/11
Realigns time-smear and applies advanced dithering
Supports MQA Labs Assurance Metadata system

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