Proof of evolution—Darwin Filters V2
As originally advertised, the Darwin architecture is infinitely evolvable, both for existing models and new ones. So far this has already been proven for new models by the introduction of first the RS6, then the RS8, RS2 and FC6, all embodying hardware refinements under the existing Darwin architecture.
Now, let’s prove this for existing models as well, by introducing an all new set of Darwin oversampling FIR filters, which will boost the performance of your existing unit (and also for new buyers) to new heights, without you spending an extra dime!
The Darwin Products Series:
What is 【Darwin Controller】?
The Darwin architecture is a new take on traditional R2R DAC technology, with modern advances including calibration / linearity correction for the R2R network above and beyond resistor matching, optional pure FIR oversampling, adjustable harmonics profile, switchable NOS / OS processing and true DSD bypass.
Summary of old filters
Up to now the Darwin system has come with a set of 10 choices of FIR oversampling AA filters. Here’s a belated brief description of each filter choice:
Default: fast normal
1-2: fast early rolloff (deep stopband rejection)
3-4: slow late rolloff (low stopband rejection)
5: NOS-like (early v.slow rolloff, negligible stopband rejection)
6-7: very fast early rolloff (shallow stopband rejection)
8-9: slow late rolloff (deeper stopband rejection)
10: minimum phase filter (slow late rolloff, low stopband rejection)
Introducing Darwin OS filterset V2
After the experience gained from real-world feedback on the Darwin V1 OS filters, and advances in computation of ideal filter characteristics, we are excited to announce the upcoming debut of the Darwin OS filterset V2! Key features include:
Default filter that is superior to old default in all technical aspects
It has cutoff frequency identical to the old filter (20800Hz), equivalent cutoff steepness, over 40dB of extra stopband rejection AND shorter time-domain footprint (shorter ringing) than the old filter. Extensive survey has also shown the zero pre-ringing characteristic of minimum phase filters to be more advantageous in preference than the zero-phase characteristic of linear phase filters, so the default filter is minimum phase.
Clear delineation of filter characteristics
We have boiled down the different preferences people have with regard to AA filtering to 3 main points, and now provide all variations on these 3 technical points in the first 8 filters:
1. Phase (minimum vs linear)
2. Cutoff slope (steep vs slow)
3. Cutoff frequency (early vs late)
(From top to bottom: Minimum phase fast rolloff, minimum phase slow rolloff, linear phase fast rolloff, minimum phase slow rolloff)
This allows any conceivable mainstream requirement to be satisfied by the first short list of filters.
3 more choices of NOS filtering
NOS is actually an umbrella term for several different approaches to "not oversampling". The existing NOS switch let you choose one of them. You may be left wanting more. Filterset V2 now comes with not one but 3 NOS filters within the Darwin filterset, allowing users to achieve the results of not one but *4* different NOS implementations!
Darwin Ultra filter
Finally, Filterset V2 comes with an ace in the hole for analog-sound lovers in the form of a new 12th filter, dubbed “Darwin Ultra”—it is the culmination of all our experience in what analog-sound lovers out in the field desire in actual sound characteristics and combine the best of NOS tonality with true OS fidelity for a new quality of sound that is OUT OF THIS WORLD (for analog-sound lovers).
Without further ado, let’s take a look at the new filterset and detailed sonic characteristics of each—as defined by true technical details rather than subjective audio feng shui adjectives!
1. Darwin Default (Minimum phase, fast-normal rolloff)
Offers high frequency bandwidth and exemplary SAF rejection for exemplary performance according to regular definitions of audio performance. Also does not have any pre-ringing of ultrasonic cutoff frequencies.
2. Minimum phase, fast-late rolloff
Compared to Darwin Default, offers further high frequency extension with slightly less SAF rejection which is fine for earphones with exemplary high-frequency fidelity. Also does not have any pre-ringing of ultrasonic cutoff frequencies.
3. Minimum phase, slow-early rolloff
Compared to Darwin Default, offers shorter post-ringing of ultrasonic cutoff frequencies for better-defined transients in exchange for lower high frequency bandwidth. The treble is more mellow and "analogue". Does not have any pre-ringing of ultrasonic cutoff frequencies, and post-ringing is less than the fast-rolloff filters.
4. Minimum phase, slow-late rolloff
Compared to Darwin Default, offers shorter post-ringing of ultrasonic cutoff frequencies for better-defined transients and does not lose high frequency bandwidth. Has lower SAF rejection instead. The treble is more pin-point accurate if played from earphones with exemplary high-frequency fidelity. Does not have any pre-ringing of ultrasonic cutoff frequencies, and post-ringing is less than the fast-rolloff filters.
5. Linear phase, fast-normal rolloff
Is linear-phase version of Darwin Default filter. Offers high frequency bandwidth and exemplary SAF rejection for exemplary performance according to regular definitions of audio performance. Also has zero phase shift across all frequencies, in exchange for pre-ringing of ultrasonic cutoff frequencies, which may be more audible than post-ringing, owing to uneven auditory masking for humans before and after an impulse. (Ringing is equal in amount to Darwin default but distributed equally between pre- and post- ringing)
6. Linear phase, fast-late rolloff
Is linear-phase version of filter no.2. Offers further high frequency extension with slightly less SAF rejection which is fine for earphones with exemplary high-frequency fidelity. Also has zero phase shift across all frequencies, in exchange for pre-ringing of ultrasonic cutoff frequencies, which may be more audible than post-ringing, owing to uneven auditory masking for humans before and after an impulse. (Ringing is equal in amount to Darwin default but distributed equally between pre- and post- ringing)
7. Linear phase, slow-early rolloff
Is linear-phase version of filter no.3. Offers shorter pre- and post-ringing of ultrasonic cutoff frequencies for better-defined transients in exchange for lower high frequency bandwidth. The treble is more mellow and "analogue". Also has zero phase shift across all frequencies, in exchange for pre-ringing of ultrasonic cutoff frequencies, which may be more audible than post-ringing, owing to uneven auditory masking for humans before and after an impulse. (Ringing is equal in amount to filter no.3/4 (less than Darwin default) but distributed equally between pre- and post- ringing)
8. Linear phase, slow-late rolloff
Is linear-phase version of filter no.4. Offers shorter pre- and post-ringing of ultrasonic cutoff frequencies for better-defined transients and does not lose high frequency bandwidth. Has lower SAF rejection instead. The treble is more pin-point accurate if played from earphones with exemplary high-frequency fidelity. Also has zero phase shift across all frequencies, in exchange for pre-ringing of ultrasonic cutoff frequencies, which may be more audible than post-ringing, owing to uneven auditory masking for humans before and after an impulse. (Ringing is equal in amount to filter no.3/4 (less than Darwin default) but distributed equally between pre- and post- ringing)
9. Non-filter
Is 1st of 3 possible implementations of an "NOS" result, other than the actual NOS switch. Non-filter does not attempt to apply any SAF rejection. Has 100% of recorded audio bandwidth and flat FR, in exchange for uncontrolled SAF. No pre- or post-ringing, actually impulse response is 2x as shartp as even the NOS switch. Uncontrolled SAF may be fine, for earphones with exemplary high-frequency fidelity. Lesser earphones (or ones with excess high-frequency bandwidth at the expense of high-frequency fidelity) may produce audible artifacts with this filter owing to IMD (or any NOS filter, but moreso with this filter than any other filter). Sound is full-band and clinically neutral, if not distorted by SAF-IMD.
10. 0th-order hold filter
2nd of 3 possible implementations of an "NOS" result, other than the actual NOS switch. Applies 0th-order hold of original signal to upsampled output resulting in the classic "stairstep" waveform response of most "NOS" systems (including also the actual NOS switch also available). No pre- or post- ringing. Has slow and widely rolled off highs, owing to the physics of 0th-order hold, which also offers some (very little) SAF rejection. Sound is more mellow, "analog" than all filters (except no. 11), if not distorted by SAF-IMD.
11. 1st-order interp filter
3rd of 3 possible implementations of an "NOS" result, other than the actual NOS switch. Applies 1st-order interpolation of original signal to upsampled signal (linearly interpolating to the next sample only). No stairsteps. No pre- or post- ringing. Has very-widely rolled off highs, which also offers some (a little) SAF rejection. Sound is the mellowest, most "analog" of all filters, if not distorted by SAF-IMD.
12. Darwin Ultra
based on long experience with R2R, NOS vs D-S, OS, we crafted the ideal oversampling filter for analog-heads. It has the same audible characteristics as the smoothest NOS filter (1st-order interp), while taking full advantage of the fidelity-increasing SAF rejection capabilities offered by oversampling. Even the phase response is new secret sauce that is superior to both minimum phase and linear phase. Such an ideal combination for analogheads is made possible only through the installable FIR system of the Darwin architecture. Analogheads, choose this and weep in joy. 😁😁😁
Glossary
SAF: Spurious Aliased Frequencies. Audio at any sample rate only defines the transducer (earphone diaphragm, etc.) position at points in time separated by the sampling period (e.g. 44100 evenly spaced samples, for 44.1kHz audio). The position is NOT defined at any times between these points prior to reconstruction, and the first step of non-OS or OS DA conversion is to assume that all other times are either zero (zero-padding) or the last known position (0th-order hold), which in either case introduces spurious aliased frequencies related to the original audio content, but "aliased" out to ultrasonic frequencies. It is usually a primary goal of a DAC to remove as much of such SAF as possible, but since SAF is ultrasonic, it might not make a difference to the sound, if the transducer (earphones etc.) reproduce ultrasonic sounds only as ultrasonic sounds. This is what happens in an NOS DAC. Paradoxically, NOS DACs (including our DACs in NOS mode) often sound like they have LESS high frequencies, because ultrasonic SAF are ultrasonic, and the 0th-order hold employed by most NOS DACs cause a rolloff in *audible* high frequencies.
IMD: Intermodulation distortion. As mentioned above, SAF may be fine to live with if the earphones produce ultrasonics, only as ultrasonics. IMD is the technical term, for when earphones have distortions in ultrasonic frequencies, and such distortions "intermodulate" with each other back into e.g. audible frequencies.
Of course, no announcement of Darwin will be complete without an overview of all the exciting features already available (in combination with the upcoming new filters):
HDR mode
Turning on the HDR switch improves the dynamic range, specifically reducing the distortion of small signals (-60dB) via a proprietary enhancement process.
Note:
1. This feature is only available on HiBy RS6 and HiBy FC6.
2. May cause issues with high frequencies in rare cases. You may turn this on and off to compare result.
NOS/OS mode
NOS mode refers to not performing digital oversampling, resulting in faster signal response and direct analog conversion of the original data. NOS mode provides a more analog-like sound.
In OS mode, you can adjust the filters to achieve your preferred sound signature.
Note:
1. The default mode is OS, but when the switch is enabled, it enters NOS mode.
2. All the features in the Darwin Controller interface are only active when in OS mode.
3. For having most of the features of NOS while having active use of all Darwin features, choose Darwin filters 9, 10 or 11 (in upcoming V2 update).
Harmonic controller
The harmonic controller primarily adjusts the second-order harmonics. Generally, the human ear prefers even harmonics over odd harmonics because odd harmonics can sound more piercing and dissonant. This aspect can be quite technical, so adjust it based on your personal preference.
Ambience enhancement
The ambience enhancement feature enhances the low-frequency components of the sound. When enabled, it adds a sense of richness and depth to the music, enhancing both the sub-bass and the overall volume perception to varying degrees.
Joint tuning mode
Joint tuning is a series of tuning configurations jointly developed by HiBy and headphone brands. It represents the recommended configurations for specific headphones on compatible players. Currently, these tuning options are available:
