DSP Sound Processing
Seltzertronics Review ADI-2 DAC FS and ADI-2 PRO FS
… in the end, once you’ve gotten used to all the corrections DSP allows, it is nearly impossible to go back. This is a game changer, even for pure music listening!
Dual 5-band Equalizer
The channel-specific dual EQ or quick bass/treble adjustments can work wonders for a speaker setup.
While no equalization as well as listening only straight linear has been a mantra for many years, research has proven that no ears are identical, and that especially in near-field listening with phones the biological differences alone make individual equalization mandatory. No two pairs of ears hear the same thing, that’s a scientific fact. Additionally personal taste makes people like different sound signatures, which can easily be copied or made more similar (equalized…) on different headphones using a good EQ. The advantages of using an EQ outweigh any alleged disad-vantages – which so often turn out to be wrong at closer inspection.
A unique feature is the ability, to setup different EQs for Speakers and Headphones and use a dual EQ with different filter curves for your left + right ears (see below).
Headphones and speaker sound profiles
The EQ provides presets including individual naming. So whatever EQ setting you need, it is quickly setup, loaded and modified. To make this feature really useful the DAC offers three individual EQ settings – one each for rear out, Phones and IEM.
With the Dual EQ it is possible, to calculate room correction filter curves for your speakers before the final DA conversion, without leaving the signal path and loosing sound quality to external devices.
These days many people suffer from hearing loss in varying degrees. No matter if it is biological, from abuse or an accident – hearing impaired is a plague of modern times. And – no surprise when thinking about it – it never affects both ears identically. The number of people having one sided hearing problems is huge, but they have learned to live with an industry that totally ignores them. Although the solution is as simple as logical – have the EQ be adjustable independently for left and right. Basically digital EQs are calculated this way, the common controls are just for making it easier to operate. The ADI-2 DAC includes an option called Dual EQ – a heaven send feature for many, for sure.
RME Audio – ADI-2 Series EQ Settings
But the awesomeness doesn’t just end here, because all of the different outputs on the RME DAC can have their own equalizer settings, so I can only have this EQ enabled on the headphone out, and you can have different EQs enabled or disabled for your IEMs, headphones, and speakers. This is such a game changing feature, because combined with ability to change channel balance when I am using this with my studio monitors, the RME DAC just completely eliminates the need for me to use the Equalizer APO software, and that is a very complicated piece of software, so the fact that you can completely replace that with an Equalizer that’s built into a DAC is something that I never thought was possible.
The ADI-2 DAC FS provides the following reconstruction filters:
Short Delay Sharp, Short Delay Slow, Sharp, Slow, NOS.
The ADI-2 DAC FS with AKM chip provides an additional SD LD filter.
The ADI-2 DAC FS with ESS chip (from mid2021) provides an additional Brickwall filter.
In most listening environments, the used filter type has no audible influence on the sound, however, the ADI-2 DAC FS provides the feature, to choose every available reconstruction filter, provided by the integrated DAC chip.
The ADI-2 DAC is using SD Sharp as the default filter, offering the most linear frequency response and lowest latency. SD Slow causes a small drop in the higher frequency range. Sharp and Slow equal SD Sharp and SD Slow, with higher latency but linear phase over the whole audio band. NOS has the smallest steepness and therefore affects treble more than the others, but offers the best impulse response. See the Technical Reference section in the manual for graphs illustrating the results in frequency response and impulse response.
If one listens to music loud, then drops the level by at least 20 dB, sound loses punch and glitter. HiFi amps tried to fight this effect by adding more bass and treble the lower the volume was set. Unfortunately that never worked as intended, and just became an additional bass/treble booster. Reason: the manufacturer of the HiFi amp could not know what volume any position of the volume knob equals at the customer’s home. Room size, room dampening and efficiency of the used speakers are all unknown.
But the effect of loss in perceived sound exists (read about the Fletcher-Munson curves), and can be easily reproduced with any serious gear by comparing normal volume and DIM state (usually -20 dB). The ADI-2 DAC offers Loudness for the analog stereo outputs, and probably is the first time that Loudness works as intended. The user can decide how much maximum gain in Bass and Treble should occur at lower volume settings. The user also sets the Low Vol Reference, where maximum gain is achieved. After extensive tests a 20 dB range has been defined as range for maximum gain to no gain while increasing volume. That seemed to be the perfect definition of the range that needs to be addressed by Loudness.
Here is an example on how it works: the user’s typical lowest level listening volume is at -35 dB at the unit. This value is now set by the user as Low Vol Ref in the Loudness menu. Then Bass and Treble Gain can be set between 0 and +10 dB. Default is +7 dB for both. Increasing the volume by turning the Volume knob causes the gain in Bass and Treble to be lowered smoothly over a range of 20 dB. So when Volume is set to -15 dB, the music is not only quite loud, but Loudness’ Bass and Treble are then at 0 dB gain. See chapter 31.6 for graphs.
No matter how sensitive the connected phones or speakers are, no matter how much increase in Bass and Treble are desired – with the ADI-2 DAC one can finally adjust it to meet the personal hearing and taste. Loudness finally works as it should have worked from the start – another unique feature in the ADI-2 DAC.
There’s also a very clever feature that RME simply call Loudness. Their thinking goes as follows: at low volumes, music tends to sound worse than it does at high volumes. This is thanks to the way we hear different frequencies at different volumes, and it can be a frustrating problem if you listen to music on low. But if you turn the ADI-2 DAC’s Loudness feature on, then drop the volume, the bass and treble gain go up by about 7dB (and you can change this number if you want). It means that even at low volumes, music loses very little of its luster.
Adjustable speaker sound perception for all headphones.
While headphones open the sound stage and make everything easier to hear and to locate by spreading the narrow sound field of stereo speakers to the left/right extreme, some people would like to have a listening situation that is more comparable to a standard speaker setup.
The RME ADI-2 DAC provides a Crossfeed effect, which reduces the artificial surround ambience that some productions have to make them sound better on speakers, but which sounds unnatural on a headphone.
Bauer Binaural method is used, with five selectable strengths of narrowing the upper fre-quencies. This advanced method, which also includes a small delay and correction of the frequency response, works quite well, and is a unique feature on a device like the ADI-2 DAC.
I love crossfeed. I use it all the time. My first serious head-amp was the Meier Corda Jazz because it had crossfeed. Usually, recordings are mixed for speakers in a stereo setup. This results in strong channel separation that can cause fatigue when listening over headphones.
For a better understanding: the mid channel represents the function L+R, while the side channel represents L-R.
During record the monitoring needs to be done in ‘conventional’ stereo. Therefore the ADI-2 DAC also offers the functionality of a M/S-decoder. The M/S-Processing automatically operates as M/S encoder or decoder, depending on the source signal format. When processing a usual stereo signal, all monaural information will be shifted into the left channel, all stereo information into the right channel (thus the stereo signal is M/S en-coded).
This was another reason for RME to offer this option in a ‘HiFi-DAC’, because the separation of the mono and stereo components provides some interesting insights into the mono/stereo content of modern music productions. Use Balance to switch between left and right only to hear the full details of the result.
It is also possible to swap channels with the -1.00 setting.
Besides the Mono settings, which sends the same signal to the left and right channels, an option is available, to send the sum of left and right channel to the left output only.
Some older CDs were recorded with Emphasis, and indeed Emphasis is part of the Red Book standard. Listening to them requires a filter on the playback side or their sound will seem too bright. The playback of older digital recordings from tape might also require de-emphasis, and even one of the first DAT recorders used Emphasis constantly.
The ADI-2 DAC FS activates the DAC’s de-emphasis automatically when the current source is AES or SPDIF and the Emphasis bit is set in the incoming Channel Status. The State Overview screen can be used to track this state, a WARNING SPDIF EMPHASIS message will be shown.
Bass & Treble
The simpler form of EQ has been the Bass and Treble controls as they are found on any ‘standard’ HiFi stereo amplifier. They easily and quickly allow to modify the sound to your personal liking (more or less Bass, more or less Treble, obviously). An even more useful application is to quickly change the amount of Bass / Treble in smaller quantities so that music compilations don’t have one song making the cones fall out while another one makes you think that really happened. Producers and mastering engineers not only have their own taste, they also sometimes fail in providing a mix that is on an average sound level compared to others. In that moment a quick turn on the two ADI-2 DAC’s small encoders will make the music sound perfect.
The Bass and Treble controls were originally limited to ± 6 dB. Everything exceeding such values should be handled by the EQ, and/or calls for better speakers/phones (due to the inclusion of B/T with the PEQ their range is now ± 12 dB). The corner frequency and quality factor of Bass and Treble is user-adjustable in the display’s menu, making this feature even more useful. Adapt it to meet your speakers/phones or your personal taste – it will greatly improve your pleasure in listening to music again.
30-band Analyzer & High Precision Stereo Meters
Thanks to the high-resolution display even smallest details are clear to see. Music content analysis is possible even when viewed from a greater distance. The Analyzer operates at any sample rate, and even with DSD from 20 Hz up to 20 kHz.
As opposed to most other solutions no FFT (Fast Fourier Transform) is used. RME’s Spectral Analyzer performs a true band-pass filter calculation, as in professional hardware devices. The frequency distance between the filters is scaled matching human hearing. The highly optimized code allows to run a 30 band analyzer with 60 dB range, sharp filters and 0.5 dB steps accuracy per band, on the ADI-2 DAC DSP, even at 768 kHz sample rate.
The most important application using a Spectral Analyzer is the visualization of frequencies and levels found in music or speech. The Analyzer shows levels and frequencies even at the edge of the human ear’s abilities – or that of the used speakers and headphone. The visual display helps to train ones ears, makes coarse errors visible, and shows what sometimes might stay unnoticed. For example many speakers won’t let you hear frequencies below 30 Hz. Simply look on the Analyzer to see what’s going on in the underground.
Stereo Level Meter
The horizontal stereo level meter below the Analyzer can show the peak level before all DSP processing (Pre, equals the current input level from USB playback and SPDIF In), after all pro-cessing including volume control (Post), or both at the same time (Dual).
Signal Check & State Overview
Adjustable speaker sound perception for all headphones.
Since 20 years RME prefers to give our customers more information at hand than just ‘something there’. The Settings dialogs of the audio interfaces include detailed Input Status analysis to simplify setup and ease trouble-shooting. Ad-ditionally RME provides a free tool with any audio interface, DIGICheck, which analyzes levels, Channel Status and bit stream content, the true hardware sample rate and much more.
When the ADI-2 DAC is connected but no sound can be heard then RME’s analysis tools come to the rescue. The State Overview screen is there to track down the problem in an easy to understand and efficient way. Although it might look simple (fully intentional!), it includes detailed analysis that outper-forms any other similar device.
Shown are the current states of the digital inputs SPDIF opti-cal and coaxial, and USB connection with the audio transmitted. The current Clock source is mentioned in full length, alt-hough this information is also found abbreviated in the status bar at the bottom.
The status bar always shows the current volume setting, the current clock source, and the current sample rate. In case of Sync problems the sample rate will either fluctuate or be shown in red – or both. This information is available in nearly all screens, and helps to get a quick overview of the current state. The State Overview screen now extends this information in great detail.
The SPDIF inputs are shown as SP op and SP co (optical / coaxial). The SYNC column shows No Lock, which equals no signal present, as – -. And lock and sync, according to the current clock state of the respective input.
USB connected is shown as soon as a valid USB connection is established.
The column SR shows the hardware measured sample rate for the SPDIF input. It will even dis-play values that can not be set at the ADI-2 DAC itself, for example 32, 64 and 128 kHz. In case of USB the sample rate is not measured but set by the external computer or iOS device, and can be verified here, up to the highest value of 768 kHz.
The State column shows the Channel Status, Consumer (cons) or Professional (pro), for incom-ing SPDIF (AES) signals. In case a DoP (DSD over PCM) header is detected DSD is shown. With USB the state column shows the current channel mode, 2/2, or DSD if a DoP header is detected.
The Bit column shows the amount of bits found in the SPDIF audio signal. Note that a 24 bit signal that is shown as 16 bit is indeed 16 bit, but a signal shown as 24 bit might contain only 16 bit real audio plus 8 bits of noise …
Before I got this DAC, I had to use a very complicated setup with many cables, but this DAC just replaced everything, AND it also replaced the Equalizer APO software that I had to use which I really wasn’t expecting as that is a very advanced software.