Importance Of Dynamic Performance

SOULNOTE Chief designer Kato continues his series of essays on design philosophy with Discrepancy between specs and sound quality.  

Previously, I have described an example of how we can predict that too high a static performance will degrade dynamic performance. This time, I would like to go further and write about an example where dynamic performance is more important to the human ear than static performance.

Static performance is performance that can be quantified and catalogued.

Dynamic performance is a time-related performance that cannot be easily quantified and can only be judged by listening.

NOS mode vs. FIR mode

Among SOULNOTE's accomplishments over the past six years, I think the most epoch-making event was the adoption of the NOS (Non Over-Sampling) mode. Moreover, it was adopted not as a special mode, but as the default mode. The sound quality has been highly evaluated, and the product is selling well in Japan.

Incidentally, the SOULNOTE D-2 has won first place in the DA converter category of Japan's most prestigious StereoSound magazine awards for four consecutive years. The S-3 Reference SACD player was selected as the reference device in StereoSound's listening room. Incidentally, SOULNOTE digital equipment can be switched between NOS mode and FIR (8x oversampling digital filter) mode with a key on the main unit or remote control. We have made it possible to switch between the two so that anyone can do a comparison experiment. (In case of USB input, some models are fixed to NOS mode.)

Now, when NOS mode is selected, Static performance is very poor.
Especially, the distortion (THD+N) value is miserable. Without bandwidth limitation, the distortion at 1 kHz is about 2%. On the other hand, when FIR mode is selected, it is about 0.005%. That's only because the analog stage is a discrete non-feedback amplifier, but still, that's a 400-fold difference in distortion! This result is not surprising since the waveform is staircase-like in the case of NOS, since there is no LPF in the analog stage. The staircase waveform, when Fourier transformed, becomes an "image signal" of 20 kHz or higher, and if analyzed with an FFT analyzer, the signal-to-noise ratio will also appear very poor. (However, I believe that the image signal is a signal to ensure temporal accuracy and not just noise. It is the frequency brain that makes it look like noise.)

Many SOULNOTE users choose the NOS mode. Why? This is because I feel the sound is honestly good. Freshness, sound image localization, and most of all, musical enjoyment! The majority of the respondents rate the NOS mode superior in all aspects. In other words, NOS mode makes it easy for everyone to experience a change in sound that Dynamic Performance may be more important than Static Performance.

Let me explain in more detail.

When observing the output waveform, in the case of FIR mode, it looks beautiful if it is a sine wave. However, with an impulse waveform, an echo is observed. This echo is an artificial waveform created by the digital filter algorithm and helps to make the staircase waveform look smooth. In other words, FIR mode is a mode that specializes in Static performance. In exchange, time-axis precision is lost. This is truly the curse of Fourier.

On the other hand, in NOS mode, the sine wave looks rattling and dirty, but the impulse waveform is very beautiful. In other words, it is a mode that specializes in dynamic performance that is faithful to the time axis. It does nothing. Just foolishly arranging the sampled data. However, many people find this sound good.

In other words, Dynamic performance sounds more natural to the human ear and resonates more with the human mind than Static performance. Why? I will write about this in the next issue.

Impulse response waveform of D-2.
Upper: FIR mode
Lower: NOS mode