DA&T’s Direct Digital System (D.D.S.): A Revolution in High-Fidelity Audio

What is D.D.S. technology from DA&T?

D.D.S. means Direct Digital System. It is the technology which DA&T developed and implemented their product line. Under D.D.S., all signals are processed in digital domain before amplification, it aims to overcome the weakest point in the entire system and deliver high fidelity audio.

Here we breakdown the philosophy of D.D.S design.

1. Rethinking Volume Control

The digitization of audio began around the 1980s with the advent of CDs and has since expanded to formats like VCD, DVD, SACD, DVDAUDIO, and BD. As we’ve grown accustomed to using computers and the internet, physical media such as CDs or tapes are gradually being replaced by digital storage and online streaming.

As traditional devices fade, should the associated equipment not also evolve? For instance, in the era of vinyl records and cassette tapes, the audio recordings were in different analog formats, and each recording medium and signal detection device produced signals with varying levels and frequency slopes, pre-amplifiers were essential for adjusting the strengths of signals from different sources, ensuring consistent signal strength and frequency response. This was the primary function of the pre-amplifier. The analog signals pre-amplifier processed then passed to the power amplifier, which drove the speakers. 

However, as CDs became the standard and other analog sources like cassette tapes declined, the role of pre-amplifiers was reduced to merely selecting signals and controlling volume, since the output from a CD player is a full-range, high-level output. This makes preamps largely redundant in a fully digital setup, leading to a debate on its necessity. This brought about the rise of integrated amplifiers, which combined the pre-amp and power amp into one unit. (from an audiophile’s perspective, there remains a common belief that a separate pre-amp and power amp setup is superior to an integrated amplifier, but from a technical standpoint, it depends.)

Imagine if the digital audio data output from an S/PDIF source was already adjusted to the ideal volume level. In such a scenario, the traditional volume knob would no longer be necessary, and this adjustment would lead to major changes in audio equipment design.

Benefits of Removing the Analog Volume Knob:

1. System Simplification: Reduces the number of components and possible sources of error.
2. Enhanced Performance: Minimizes distortion, especially from wear-prone analog components.
3. Environmental Friendliness: Fewer materials needed in manufacturing.
4. Changes in User Interaction: Users adapt to a streamlined digital experience without the traditional volume control.

2. System Simplification

With D.D.S., volume control happens entirely in the digital realm. Using a advanced 32-bit digital volume processing and removing the need for analog potentiometers, D.D.S provide several benefits.

• Elimination of Analog Distortions: Analog potentiometers, no matter how well engineered, have inherent limitations due to their resistive properties. By moving volume adjustment away from analog potentiometers, D.D.S. avoids distortions caused by component inconsistencies. 
• No Component Degradation: Digital volume control doesn’t suffer from the wear and manufacturing errors that affect analog components over time, ensuring reliable performance.
• Extended Dynamic Range: Achieves up to a 130dB dynamic range, far surpassing the capabilities of traditional analog controls.
• Precision in Volume Adjustment: Digital calculations allow for extremely accurate adjustments, preserving sound quality even at low volumes.
• Minimal Quantization Errors: The 32-bit system handles calculations with high precision, reducing errors that would typically arise in 16-bit analog systems. This results in a more natural and immersive listening experience.

With D.D.S., there is no need for separate pre-amplification in a purely digital system. Audio signals from digital sources can be processed directly without converting to analog until the final amplification stage. This simplifies the system and reduces the number of components, leading to higher fidelity sound and a more compact design.

3. Why 32bit Processing? 

The master recording for a CD may be in 24-bit, but the CD itself is limited to 16-bit. Before 32-bit processing methods were developed, using digital means to control volume yielded unsatisfactory results. This is because 16-bit recording only captures a dynamic range of 96dB, and within this relatively limited dynamic range, any calculations involving parameters inevitably result in significant errors.

Clearly, using 16-bit calculations and decoding within a 16-bit recording format is far from ideal. Expanding 16-bit to a higher bit depth, such as 32-bit, allows for mathematical techniques that retain 16 decimal places. This effectively utilizes the 192.6dB dynamic range of 32-bit processing to handle the 96.3dB dynamic range of 16-bit audio, resulting in errors so minimal they are almost negligible. Today’s best digital processors offer a quality within a dynamic range of approximately 130-140dB. In short, even if there are minor errors when using 32-bit calculations for 16-bit audio, these errors fall well outside the 140dB dynamic range that current technology can reproduce.

The 32-bit processing technology is how D.D.S. achieve the acclaimed precision in digital processing.

4. Upsampling and Filtering for Enhanced Signal Processing

By upsampling the original sampling rate—such as from 44.1kHz to 352.8kHz—D.D.S. (Direct Digital System) allows digital processing to create smoother, more continuous waveforms, which directly reduces perceived distortion. This eightfold upsampling transforms the digital signal, dividing quantized values into smaller segments and applying predictive algorithms to reconstruct smoother curves. As a result, the audio signal’s waveforms become more refined, approaching the smoothness of the original analog signal.

Digital filtering is another essential part of this process. Modern 32-bit processors, capable of high sampling rates like 384kHz, allow for sophisticated filtering techniques. By processing the audio signal at higher frequencies, digital filtering helps minimize phase shifts and unwanted aliasing effects that occur when lower sampling rates are used. High-frequency digital filtering prevents high-frequency noise from entering the audible range, ensuring the sound remains natural and clear.

5. Ground Isolation

In electronic circuits, “ground” refer to the “ground” potential within a circuit, typically at zero volts. This 0V reference point is essential for all calculations in electronic circuits. Ideally, ground would be a perfectly clean, straight line with no fluctuations. However, in reality, no conductor has absolute zero impedance, meaning parasitic capacitance and inductance are inevitably present.

When current flows through resistance, it creates a voltage difference; when it crosses inductance, it generates an electromotive force; and when electrons accumulate in capacitance, it creates charge. These tiny voltages become undesirable and unavoidable signals for the amplifier, which means, they are noises, in analog.

While the analog noises from one single device seems small and insignificant, the complex process in audio playback involves signal conversion, processing, and amplification. Each component in the chain receives the ground noise from the previous component, results in accumulation of the noises. When the system contain many devices, it forms a tangled web of wires, and many potential ground noise sources.

Amplifiers are fundamentally designed to “amplify.” They take the vibrational energy from analog sources (e.g., a turntable) and convert it into electrical energy. This electrical signal often measures only millivolts or microvolts and is then amplified enough to drive the speakers. During amplification, any ground noise from earlier components is also amplified.

For the amplifier to obtain ideal sound quality, analog noises should be minimized but that is hard to achieve. Here comes D.D.S., a simple and elegant solution for tackling ground noises. Digital processing does not have these tiny analog signals. Instead, there are a series of “0” and “1” signals, recorded and transmitted as distinct high and low voltage levels.

This clear voltage difference can be converted into light (as in optical fiber) or coupled electronically, which breaks the connection between the ground of different devices. With this separation, the ground noise problem is resolved since digital transmission doesn’t rely on a shared ground reference. By keeping all signals digital until the final stage of the amplification, the amplifier can focus solely on amplifying the intended signal, minimizing ground interferences.

6. Reduced Gain and Noise

Gain generally refers to "amplification factor." For instance, in a system with 100W power and an 8-ohm load, the voltage swing would be 40Vp. If the DAC (Digital-to-Analog Converter) outputs 2.8V, an amplification factor of only 15x is needed.

In traditional audio systems with separate pre-amplifiers and power amplifiers, the preamp’s gain is around 20dB (10x amplification), while the power amp’s gain is typically 30-35dB (30-60x amplification). When combined, the total gain can reach 300-600x. However, this high level of amplification not only amplifies the music signal but also any noise present.

This high amplification arose from compromises made over time to accommodate various audio sources and ensure compatibility within the market. Manufacturers adopted these standards to maintain compatibility, but this also restricted potential improvements in audio quality. For example, after the 1980s, CD players were designed with a 2V analog output, theoretically allowing direct connection to a power amplifier. However, traditional setups connected the signal to a preamp, where it was first attenuated by a volume resistor, then amplified by 20dB, before being sent to the power amp for further amplification. Even with the best circuitry and components, this process inevitably introduces unwanted modulations, resulting in new distortions or interferences. At best, these may alter the tone; at worst, they degrade audio quality.

The D.D.S. (Direct Digital System) concept addresses this by performing volume calculations and adjustments at the digital signal source itself. This approach eliminates the need for analog potentiometers to control volume across channels. Without an analog volume control, the subsequent 20dB preamp amplification stage is also unnecessary, allowing the DAC’s output to connect directly to the power amp. Thus, an amplification factor of only 15x to 35x is sufficient. With fewer amplification stages, there is less distortion and less unwanted interference, leading to a purer audio signal.

7. Monophonic Design and Crosstalk Elimination

If we had to decide on the layout under a fixed distance for placing a power amplifier, should the signal cable be shorter and the speaker cable longer, or should the speaker cable be shorter and the signal cable longer?

In this situation, choosing “long signal cables and short speaker cables” is the better option. Here’s why:

1. Low Impedance and Impedance Variations: Speakers typically have low impedance (around 4 to 8 ohms) and significant impedance fluctuations. Longer speaker cables might have a noticeable impact on sound quality, potentially introducing changes that are difficult to correct.

2. Reduced Interference: If the signal being transmitted over a long distance is digital, it has less impact on sound quality because digital signals are less affected by cable length. However, speaker cables carry amplified analog signals, which are more susceptible to impedance, capacitance, and inductance effects. Keeping speaker cables short minimizes interference and enhances sound quality.

Iff we design the amplifier as a monoblock unit with a built-in monaural DAC (Digital-to-Analog Converter), the amplifier can be positioned right next to the speaker, keeping speaker cable transmission to a minimum. This setup could even involve integrating the amplifier directly within the speaker cabinet, a great solution for modern living spaces as it saves considerable room by eliminating bulky external components.

Traditionally, to ensure synchronized volume control across channels, stereo or multi-channel analog signals are processed within a single chassis, sharing a common power supply and ground. This setup often leads to severe crosstalk, where interference between channels varies depending on volume level. Contrary to popular belief, crosstalk distortions does not only occur in higher volumes; in fact, it is a serious problem at typical listening levels.

With a monophonic (single-channel) design, crosstalk can be significantly reduced or even eliminated altogether. This is because the digital-to-analog conversion can be configured to decode only one specific channel (e.g., left or right), ensuring that other channels are entirely absent from this path, thus preventing any potential crosstalk.

8. Achieving a 130dB Dynamic Range

D.D.S. enables an uncompromised dynamic range of up to 130dB, far exceeding what traditional analog systems typically deliver. This high dynamic range ensures that audio is reproduced with full fidelity, allowing listeners to experience details across both loud and quiet passages without distortion or noise interference. The benefits include:

• Full Audio Fidelity: By maximizing the dynamic range, D.D.S. maintains both powerful and delicate sound details, giving listeners a richer, more immersive experience.
• Noise-Free Playback: The minimized noise floor in D.D.S. prevents background noise from interfering with audio playback, resulting in a cleaner, more authentic sound.

Conclusion: The Future of High-Fidelity with D.D.S.

DA&T’s Direct Digital System (D.D.S.) is a comprehensive solution that transforms audio processing by addressing the limitations of analog systems. By fully digitizing volume control and eliminating analog-related distortions and noise, D.D.S. delivers superior sound clarity, greater channel separation, and enhanced reliability. This technology marks a new era in high-fidelity audio, paving the way for simpler, more efficient, and environmentally friendly audio systems without sacrificing sound quality.

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