Why USB Cables Can Make a Difference。为何USB线有差异。

音乐之贼 1月前 19

David Salz, Wireworld
Are USB cables really just 1's and 0's traveling down a wire? If not then what? Digital signals are actually square waves that are detected by the receiver when they pass a voltage threshold. Any variation in the shape or timing of these waveforms can cause errors in these signals.
How sending a file of music is different than that of an image to print? It is just data after all. When a file is saved or sent to a printer, the error correction system in the receiving device can ask the sending device to resend the file until it confirms that the file is completely correct.
Streamed music signals do not benefit from this resend function and therefore error correction systems cannot replace missing or corrupted data.
What is happening inside a USB cable that could impact the sound or information being transmitted? The normal losses of cables will round and tilt the signal waveforms, creating data errors that cause audible losses, tonal coloration and distortion. Those losses and colorations can easily be heard when standard USB cables are compared to reference adapters made from USB plug contacts soldered back-to-back. Designing a USB cable for minimal loss and maximum waveform fidelity is the only way to minimize these losses.
Separate power and signal? Computer power supplies are notoriously noisy and that noise can compromise the fidelity of USB audio. Most USB cables do not isolate the noisy power conductor from the signal conductors, so noise can mix with the signal and it can also enter the DAC through the 5 volt USB power conductor. Therefore, the 5 volt conductor needs to be isolated from the signal and filtered of noise or replaced by a separate quiet power source.
Noise? Noise can also be generated from static charge interaction within the cable. This triboelectric noise adds roughness to the signal waveforms. That roughness creates additional timing errors (jitter) in the signal. Reducing this noise enables cables to sound closer to the purity of the reference direct connection.
Marcin Ostapowicz, JPLAY
1's and 0's are logical interpretations of voltage signals. USB signals are transmitted using differential signaling: for USB 2.0 signal levels are −10–10mV for logical low and 360–440mV for logical high level. So basically we are dealing with a very sensitive electrical (analog!) signal. High data rates of USB 2.0 result in jitter and attenuation becoming a major problem (higher frequencies attenuate faster than lower frequencies over distance. Additionally, higher frequencies are more susceptible to jitter). Degradation in the signal can be seen as it travels from a transmitter (PC) to a receiver (USB input in DAC). Reflections and clock inaccuracies cause jitter which closes the so called eye-pattern and makes the signal less readable. Music playback is a real-time process where accurate timing is everything, so it is extremely important to minimize jitter. We use these techniques in our cables to maintain signal integrity:
1) Reduce the capacitive reactance and inductive reactance to make the signal impedance reduce more accurately.
2) Considering the skin effect we only use very slim conductors.
3) We use triple shielding to prevent EMI. CPU speeds in PCs are up to few Gigahertz. It will emit a lot of electromagnetic radiation that's within the frequency range of USB signal.
In our top USB cable we also introduced a dual-lead design that separates the USB data lines from the power line. Each line has a separate USB type A connector with the dual lines terminated with a single USB type B connector. That plus double-shielded solid aluminum connectors results in better sound quality and a lower noise floor.
最新回复 (7)
  • Jedibosin 1月前
    引用 2
    Wireworld的David Salz
    Marcin Ostapowicz,JPLAY
    1和0是电压信号的逻辑解释。USB信号使用差分信号传输:对于USB 2.0,逻辑低电平为-10-10mV,逻辑高电平为360-440mV。因此,基本上,我们正在处理非常敏感的电(模拟)信号。USB 2.0的高数据速率导致抖动和衰减成为一个主要问题(较高的频率在整个距离上的衰减快于较低频率的衰减。此外,较高的频率更容易受到抖动的影响)。从发射器(PC)到接收器(DAC中的USB输入),可以看到信号的衰减。反射和时钟的不准确会引起抖动,从而使所谓的眼图关闭,并使信号的可读性降低。音乐播放是一个实时过程,其中准确的时间就是一切,因此,最小化抖动非常重要。我们在电缆中使用以下技术来保持信号完整性:
    在我们的顶级USB电缆中,我们还引入了双引线设计,该设计将USB数据线与电源线分开。每条线都有一个单独的USB A型连接器,双线以一个USB B型连接器端接。加上双屏蔽实心铝制连接器可带来更好的音质和更低的本底噪声。
  • 战斗天使 1月前
    引用 3
  • fjtdrf2004 1月前
    引用 4
    战斗天使 发表于 2020-9-18 15:20
    测量 出来 能说明那个更好听么? 如果不能,除了证明有变化之外还有什么意义。
  • erjinetac 1月前
    引用 5
  • 姚鹏 1月前
    引用 6
  • yeeypc 1月前
    引用 7
    erjinetac 发表于 2020-9-19 00:56
  • allenwong 1月前
    引用 8
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