42bit数字音量可以PK模拟音量吗？

kingcole

德国专业品牌RME一款针对HIFI市场的新款旗舰ADDA解码 ADI-2 pro，其长长的说明书中提到了42bit数字音量，并附有测试图，一个CD 16bit/44.1的数字信号，数字衰减-40db后THD仍有-130db，可以说在数字处理部分是可以完全平移CD信号的动态了，如果DAC输出的模拟底噪（这台 ADI-2 pro按官方Signal to Noise ratio (SNR) @ +4 dBu: 115 dB RMS unweighted来换算，noise是-111dBu（2.18uV））与外部模拟前级的模拟底噪一致时，那是否可以与模拟前级PK一下了？下面是摘自官方说明文档原文：
http://www.rme-audio.de/download/adi2pro_e.pdf   （87-88页）


34.20 Digital Volume Control
The ADI-2 Pro deliberately avoids an analog level adjustment by means of a potentiometer. Its
digital version surpasses an analog one in practically every conceivable point. Typical
disadvantages of setting with potentiometers:
• Synchronicity errors lead to panoramic shifts and significant volume deviations left / right, in
particular near the end points of the adjustment range.
• In the middle setting range, there is an increased crosstalk and changes in the frequency
response. Changes in the frequency response also occur at the end regions of the
adjustment path.
• The setting range for optimum volume adjustment is often too small, or at the lower or
upper end of the potentiometer's adjustment range.
• Non-reproducible settings (except 0 and 11).
• Higher THD/THD+N. A point well known to measurement technicians. As soon as an
analog potentiometer is in the signal path, the unstable contact between wiper and resistive
track causes noise, which contains both THD (noise) and N (noise), even in the stationary
state. Thus the -110 dB of a DAC quickly get reduced to -80 to -70 dB.
Special volume ICs, which activate different resistance values by means of numerous electronic
switches, avoid some of the above mentioned points. Unfortunately, even the best of these ICs
do not achieve either THD or dynamics of the DACs used in the ADI-2 Pro, thus would affect its
analog output signal.
However, none of this is an issue with RME's digital volume control!
In fact an analog volume control has a (theoretical) advantage in only one point, namely the
maximum signal to noise ratio at a higher level reduction. In reality, current circuitry overturns
the theory, and the SNR at the output of such a device is no better than that of a digitally controlled
one. This is even more true the better the DA converter works and the less noise it has -
just like the ADI-2 Pro, which provides the maximum noise ratio over a wide level range of 20
dB, thanks to its four reference levels realized in the analog domain.
The most often cited issue of a digital volume control is an alleged loss of resolution at higher
attenuation. An example: 117 dB dynamic roughly equals 19 bit resolution. A volume attenuation
of 48 dB (8 bit) leaves 11 bit of resolution. Such a simple, but important details omitting
argumentation, usually ends with: the music must sound distorted in quieter parts, and the signal
to noise ratio is down to a useless 69 dB.
The former is simply wrong, the latter irrelevant in practice. Indeed there is a reduced signal to
noise ratio, but it doesn't matter, as the noise was not audible before (below the hearing threshold),
and is still not audible after lowering the level. And the reduced SNR also applies to
devices with potentiometers, since the potentiometer is never placed at the output, but in the
middle of the circuit, followed by further electronics which also add some basic noise.
The quality of the ADI-2 Pro's digital volume control is best shown by measurements. Hard
times coming up for convinced supporters of the analog control, because here it is very clear
that the disadvantages of a digital volume adjustment, such as roughness and distortions at
higher attenuation, simply do not exist - at least with RME.



The following measurement shows a digital full-scale sine of 1 kHz, 16 bits without dither, which
is reduced in level by 40 dB. Also shown are a full-scale sine of 1 kHz with 24 bit, at 60 dB and
96.3 dB level attenuation, which is the lowest volume setting the ADI-2 Pro offers.
A high-resolution FFT like HpW Works makes it possible to disassemble the signal into
individual frequencies, and to identify unwanted components down to a level of -190 dBFS. The
measurement shows that the undithered 16 bit signal does not produce any distortion or other
tones above -170 dBFS. So at a volume setting of -40 dB the measurable THD is -130 dB. At 24
bit a volume setting of -60 dB also achieves -130 dB without distortion. And at a volume setting
of -96.3 dB there are still -93 dB THD measurable.





These results clearly show that distortion products of the digital volume control are not drowned
by the DAC's noise, but are not generated at all. It works perfectly even with an undithered 16
bit signal, no detectable distortion products are produced.
If the volume control is measured at the analog output, the demonstrable THD is reduced to
around -100 dB at a volume setting of -60 dB, by the self-noise of the DAC (SNR 117 dB RMS
unweighted). In the above measurement that would be seen as straight noise floor at -160
dBFS. The digital volume control of the ADI-2 Pro therefore works much more precisely and
cleaner than required for current top-level DACs.
In summary:
RME's digital volume control in 42 bit TotalMix technology avoids all the disadvantages of
analog level control via pots, is easy to use, offers reproducible settings, and the highest sound
quality.





ADI-2 pro官方参数：
Technical Specifications

Analog Inputs
XLR
• Input: XLR, servo-balanced
• Input impedance balanced: 18 kOhm, unbalanced: 9 kOhm
• Input sensitivity switchable +24 dBu, +19 dBu, +13 dBu, +4 dBu @ 0 dBFS
• Digital Trim Gain range: 0 dB up to +6 dB
• Signal to Noise ratio (SNR) @ +13/19/24 dBu: 120.x dB RMS unweighted, 124.x dBA
• Signal to Noise ratio (SNR) @ +4 dBu: 119 dB RMS unweighted, 123 dBA
• Frequency response @ 44.1 kHz, -0.1 dB: 5 Hz – 20.5 kHz
• Frequency response @ 96 kHz, -0.5 dB: 3 Hz – 45.5 kHz
• Frequency response @ 192 kHz, -1 dB: 2 Hz – 92.7 kHz
• Frequency response @ 384 kHz, -1 dB: < 1 Hz – 124 kHz
• Frequency response @ 768 kHz, -3 dB: < 1 Hz – 180 kHz
• THD @ -1 dBFS: -116 dB, 0.00016 %
• THD+N @ -1 dBFS: -112 dB, 0.00025 %
• Channel separation: > 110 dB

Analog Outputs
1/2 XLR
• Output level switchable +24 dBu, +19 dBu, +13 dBu, +4 dBu @ 0 dBFS
• Signal to Noise ratio (SNR) @ +13/19/24 dBu: 117 dB RMS unweighted, 120 dBA
• Signal to Noise ratio (SNR) @ +4 dBu: 115 dB RMS unweighted, 118 dBA
• Frequency response @ 44.1 kHz, -0.1 dB: 0 Hz – 20.2 kHz
• Frequency response @ 96 kHz, -0.5 dB: 0 Hz – 44.9 kHz
• Frequency response @ 192 kHz, -1 dB: 0 Hz – 88 kHz
• Frequency response @ 192 kHz, -1 dB: 0 Hz – 88 kHz
• Frequency response @ 384 kHz, -1 dB: 0 Hz – 115 kHz
• Frequency response @ 768 kHz, -3 dB: 0 Hz – 109 kHz
• THD @ -1 dBFS: -112 dB, 0.00025 %
• THD+N @ -1 dBFS: -110 dB, 0.00032 %
• THD @ -3 dBFS: -116 dB, 0.00016 %
• Channel separation: > 110 dB
• Output impedance: 200 Ohm balanced, 100 Ohm unbalanced

ouyangbo

这个东西太专业不好回答，我只能打个比喻，人造处女膜就算做得再逼真但始终是人造的

卡西利亚斯

我还能做到256bit的无损数字音量呢，问题是DAC能解决么

kingcole

卡西利亚斯 发表于 2017-5-10 10:47
我还能做到256bit的无损数字音量呢，问题是DAC能解决么

dac与模拟前级同样受限于自身底噪的水平

kingcole

按理要比直接调dac芯片内部的数字音量要好吧

markamp

不管输入是16bit还是42bit，进入DAC后，量化误差都是24位(对于24bit ADC)

markamp

DAC

markamp

内部音量也是

swing

kingcole 发表于 2017-5-10 11:04
按理要比直接调dac芯片内部的数字音量要好吧

试过90x8音量调节，妥妥的，一点问题都没有。

kingcole

markamp 发表于 2017-5-10 19:12
不管输入是16bit还是42bit，进入DAC后，量化误差都是24位(对于24bit ADC)

这款解码用的是AK4490，是32bit的

zoozooo1

只能静等技术突破

xmlhifi

音量功能在不用调整的时候，是没有用的功能，只要负面的影响，因此说是一种累赘。

gxhj

太专业的东西理解不了。不过RME的东西在专业里小有名气了，东西稳定，性价比高。尤其是声卡，驱动很稳定，功能强大。只是在纯ADDA方面好像只能排三线。

kingcole

gxhj 发表于 2017-5-11 22:03
太专业的东西理解不了。不过RME的东西在专业里小有名气了，东西稳定，性价比高。尤其是声卡，驱动很稳定， ...

一线DA如果没好的前级，最终效果可能还不如三线。而真正好的前级都不比这些DA便宜

kingcole

这个ADI-2 pro是目前rme的顶级了，号称是针对hiend市场的，相信有一定素质才敢拿出手的。只是国内用户太少，没多少评价。国外的论坛倒是有一些评论，毕竟这机器才上市不久。看国外评价应该是与prismsound Lyra和lynx hilo一个档次的机器