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Quality first: Creating the AXR4 audio interface series

Interviewee: Yamaha AXR Development team

Steinberg AXR4 audio interfaces set a new standard for professional studios, producers and musicians. The development team’s intention was to deliver the highest possible audio quality, along with flexible features that would make the AXR4 series the ultimate solution for a wide range of recording applications. In this interview they discuss how these remarkable audio interfaces were developed.

The development of the AXR4 audio interface series has seen Yamaha engineers working tirelessly to create professional-level units, which deliver the highest possible audio quality. The development team speaks about their design approach and the challenges they faced in bringing these exceptional units to market.

For many years Steinberg has developed and refined legendary recording applications like Cubase, with the best recording engines and most flexible arranging and editing tools. But those benefits are compromised if the audio interface is not of a similar high quality. As one of the most critical parts of any recording system, if the audio interface is not up to scratch, your recordings will never be as good as you want them to be.

For the past 15 years, Steinberg has worked closely with Yamaha to produce audio interfaces which maximize the recording quality in any situation. With the AXR4 series, professional studios, engineers and musicians now have a solution which delivers unsurpassed audio quality, with features that can handle even the biggest sessions. The result of a long and very painstaking development process, this is the story of how the AXR4 series was created.

The AXR4 has a number of noteworthy features, including 32-bit integer AD/DA converters that support sample rates up to 384 kHz, digital emulations of SILK processing from Rupert Neve Designs, a full matrix mixer using dspMixFx, and internal DSP that allows near zero- latency recording and monitoring. From an engineering standpoint, what do you feel is the most important feature?

We always take the needs of a broad cross section of audio interface users into account and try to respond to as many as we can, but in the case of the AXR4 our main priority from initial planning right through the development process was to achieve the highest possible sound quality.

Can you give us a specific example?

For example, after repeated listening tests we realized that the 32-bit integer 384 kHz AD/DA converters we eventually chose had better low-frequency imaging and overall sonic definition than any of the others we tested, and were determined to use it in the AXR4. High cost made it difficult to justify, but we refused to use cheaper converters because sound quality was our primary concern.

Tomoyuki Hayashi, GUI Software Group, MX Development Department

But sound quality is not determined by AD/DA converters alone?

Of course. AD/DA converters are just one element. The AXR was designed with top-quality components from input to output, and we did everything we could to bring out the full potential of the entire system.

What aspects of the AXR4 exemplify that high quality?

Keisuke Mikata, Electrical Design Group, MX Development Department

One example is the microphone preamplifiers. The preamps themselves are Yamaha designs that employ the latest and greatest technology throughout, so their performance is top class. The AXR4 preamps additionally feature Yamaha VCM (Virtual Circuit Modeling) emulations of Rupert Neve Designs SILK processing. There are a number of plug-ins on the market that attempt to replicate the Neve sound, but our SILK processing emulation employs original technology to deliver performance that is indistinguishable from the actual circuit. In fact, we are authorized to use the SILK name with the explicit approval of Mr. Rupert Neve himself and the engineers at Rupert Neve Designs.

After extensive listening tests they are fully satisfied that we have accurately recreated the SILK sound. There are two SILK variations: “Red” and “Blue,” each delivering a different type of transformer sound that can be finely adjusted in 100 steps. The AXR4 preamps can accurately capture the source sound as it is, or add varying degrees of “character” for recordings that reflect the highest quality standards.

With microphone preamplifiers that include SILK processing, plus a DSP mixer that allows reverb and compression to be applied to the monitor sound while recording with near zero latency, it seems that the AXR4 is primarily designed for engineers and musicians who are concerned with recording quality. Is that an accurate assessment?

Some of the factors we consider indispensable when designing an audio interface include basic performance, such as mic preamp quality and character, and the flexibility needed for a smooth recording workflow. But for the AXR4 our main focus was always to achieve the highest possible sound quality. That is one of the reasons we started the design from scratch. During the early AD/DA converter selection process we were simultaneously discussing 32-bit integer support for Cubase, Nuendo, and WaveLab with Steinberg. A 64-bit float mixing engine was introduced with Cubase 9.5 in 2017, with support for 32-bit integer recording and playback to be added in a later update.

Takehiro Yoshida, Electrical Design Group, MX Development Department

The DAW must provide 64-bit float internal processing in order to maintain the full resolution of 32-bit integer recordings. Coming back to the AXR4 hardware, we made no compromises in the analog circuit design while carefully considering and balancing compatibility between each and every component. We also implement SSPLL, our original jitter reduction technology, to ensure that digital input jitter was reduced to an absolute minimum. All of these elements add up to an organic whole that offers extremely high sonic quality for sound design, mixing, mastering, and other sound-critical applications.

Some people say that the low-level audio signals captured by 32-bit integer recording are masked by the noise floor?

Ryohei Koga, Electrical Design Group, MX Development Departmet

That might be the case if you are thinking in terms of the dynamic range available with analog circuitry, but we believe those subtle levels are an essential part of the sound. When recording analog sound, it is important to capture as much of the sonic information as precisely as possible. The more information you miss, the less accurate the reproduction will be. Definition and imaging will suffer. A 32-bit integer recording captures more sonic subtleties so that, for example, the sense of “air” that harmonically rich sounds often have can be effectively reproduced. We were able to hear that effect clearly during development, while experimenting with mixing 32-bit integer recordings of different instruments.

Many of the latest DAWs have 64-bit float mixing engines, but the advantages of that format can only be fully realized through 32-bit integer recording and playback. At the current time, the only programs that offer a 64-bit float mixing engine plus 32-bit integer recording and playback are Cubase, Nuendo, and WaveLab. But overall quality depends on more than just the digital domain, so the analog circuitry in the AXR4 has been designed without compromise to ensure that the potential of 32-bit integer recording and playback is fully realized.

Is the AXR4 suitable for applications other than music production?

The AXR4 is one of the highest-quality audio interfaces currently available. Its ability to accurately capture and reproduce sound is not only ideal for music production, but can also be a huge advantage for audiophiles who want to archive their valuable record collections.

Akio Yatsui, Mechanical Design Group, MX Development Department

In conclusion, is there anything else you’d like to say to our readers?

Firstly, I’d like to thank everyone who has read the interview right through to the end. And as I have already mentioned, the AXR4 has been specifically designed to achieve the highest audio quality currently conceivable in an audio interface. Many challenges had to be overcome in the process of bringing this dream to fruition, from initial planning right through to manufacture, and that meant that development took longer that it normally would. To us, the AXR4 is a very special product that we are able to deliver to our customers with the utmost confidence. We sincerely hope that many users will take advantage of the substantial benefits it provides.