RME Fireface 400

Audio quality tests of the analog section

We've used the following devices in our comparison:

The LynxStudio Aurora 8 was used as a reference device and a switchboard to reroute signals to the ADAM S2.5A monitors. We've carried out an experiment in order to find out whether the Aurora analog section distorts signals from devices - we compared the signal at the monitors with the signal routed through the Aurora. We've heard no difference, as in case with changing Aurora channels. But signals from connected devices were noticeably different.

Our tests were carried out by our test procedure, which complies with AES20-1996/2002 in many respects (it's available for AES members).

AES20 requires double blind tests (DBT). (AES20-1996/2002 7.10.1.) They must be based on recordings with recognizable tones of musical instruments without heavy sound processing. (AES20-1996/2002 6.2.2). Test fragments must be approximately 10 seconds long, a pause between fragments must not exceed 5 seconds, then you must switch to the original track and back. The longer is the pause between fragments, the less adequate the results, because the man does not have long-term aural memory. If the pause is long, only emotional reminiscence remains, no audio details can be recollected. The volume of compared signals must be absolutely identical.

We used the following sound tracks:

1. Vaclav Nelhybel - Trittico - Allegro Maestoso (16 bit 44.1 kHz)
2. J.S. Bach - Gavotte In D Minor - Jacques Loussier Trio (16 bit 44.1 kHz)
3. Latin Jazz Trio - Mujaka (24 bit 96 kHz)

We also used a ready commercial project to test the Fireface 400 in professional sphere: adjusting effect levels in a downmix, changing instrument tones in different tracks. In this case we test how adequately the section can reflect the smallest changes in a sound track.

The RME Fireface 400 interface demonstrates high professional audio quality. There are no tonal distortions, a good detailing level. The Fireface 400 outscores the ESI Juli@ and is slightly inferior to the 1616M and Aurora 8 in quality of the analog section. You can also consider the Fireface 400 as a cheaper modification of the Fireface 800 with the same functionality, but with fewer analog interfaces and converters of the high but not top level. Nevertheless, quality of the new codecs pleasantly surprised us even as we tested the ECHO Audiofire. Devices based on the AK4620A outperform units with separate converters offering similar characteristics. We have information that RME initially planned on using separate DAC and ADC. But having heard the quality of new AKM codecs, they were impressed and decided to use them. Anyway, if you choose higher quality of the audio section and more mic-ins, you should choose the Fireface 800 (119 dBA).

This device also demonstrates advanced functionality for recording. When two capacitor microphones were plugged, one of them (usual) required phantom power, the other (tube model) was powered from its own PSU. The RME Fireface allows to apply phantom power only to one microphone input, while many devices apply +48V to all inputs at once to facilitate the design process.

When you work with the mixer, it's convenient to see exact values (to within 0.1) of faders as well as peak meter values of channels. The latter offers flexible and really useful settings. For example, it allows to choose a meansquare/peak level with a 3dB RMS compensation. These values are computed not by the driver, but by the built-in hardware DSP.

Measurements

We test the RME Fireface 400 in loopback mode, so that we can compare its results with other devices. Readings with the Lynx Aurora are close to the data published in the specifications. The noise level is -113.2 dBA, while the specs mention 113 dBA. THD+N at the 5/6 output is 98.7 dB (unbalanced), this value also matches the one in specs (<-96 dB).

Detailed report on the RME Fireface 400

The level of harmonics on the distortion graph is plotted for -3 dB FS, while the value depends much on the amplitude. It's the worst case, distortions for input and output separately are lower, they match the ones published in the specifications.

We should also examine the question of jitter and its suppression. The Fireface 400 uses a digital reference generator, which gives flexibility in finetuning playback speed in professional applications. According to the specifications, the interface jitter is low, and the spectrum is uniform. But purists interested in extremely low jitter will prefer devices based on a high-quality crystal oscillator with a fixed reference frequency. The Fireface 400 is not designed for audiophiles, its architecture is not optimized for that. It's not justified to use this device as a stereo interface for audio output.

Leaning upon the article "Jitter. Theory. Part 3", written by Julian Dunn, published in Audio Precision, we can analyze loopback vs. line out graphs. Our tests reveal decreased rms of the dynamic range at several dB with a test signal because of a wide-band jitter. It may be the cost of the digital tunable clock oscillator. Clock oscillators of playback (RME Fireface 400, 800 ps) and record (Lynx Aurora, 20 ps) devices were not synchronized. The difference between the signals on the graph and the 12 kHz sine is definitely not noise or interferences, because the noise threshold is expectedly higher on the noise graph in the loopback mode. It's a good test, but it requires two devices, one of which should have a more precise clock oscillator.

In this case the results are beyond our hearing, considering the wide-band spectrum - just like in the specifications. If we compare results of the Fireface 400 with those of the ECHO Audiofire 4, the ECHO has more problems with low-frequency jitter. Fortunately, even such problems of the Audiofire 4 do not affect the resulting audio quality - jitter grows exponentially to frequency. We must always combine measurements with psycho acoustic aspects of perception - LF jitter is beyond hearing up to 200 ns.

We've heard no problems of the Fireface 400 with jitter. Differences from the other devices are conditioned only by the converters. Measurements with the APS2 show that they determine signal/noise of a device and distribution of its harmonics.

Conclusions

As it's difficult to stick to the principle of reasonable sufficiency, many beginning sound producers and computer musicians seek devices with incredibly high parameters, while the rest of the audio section, monitors in the first place, do not match even the cheapest interface. But they won't hear any difference between converters of the mastering level and semi-professional devices. Functional peculiarities and usability reserve unpleasant surprises for later.

In this respect, the RME Fireface 400 seems to be sufficient for 90% of High-End equipment in terms of its analog section quality. Its functionality and convenience are sometimes much higher than in its competing products. Besides, although the price of the RME Fireface 400 is not quite affordable for enthusiasts, it can be recommended to commercial studios even with low budget. Features of the Fireface will be excessive for beginners who own only "monitoring" headphones for $100. They'd better choose simple dual-channel interfaces for $150 from manufacturers of semi-professional equipment. They should acquire some experience before they start using a hardware mixer in stand-alone mode, multi-channel recording with individual submixes, as well as a logarithmic analyzer, time-code support, and other things.

The RME Fireface 400 is not an advanced modification of a cheap interface for an impressive price, which will demonstrate striking quality with the $100 audio section and will automatically downmix your composition with a hardware mixer. It's a professional tool for those people who really need it, in the first place.