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| [#1] Femto Clock 慢慢會成為DAC必要既東西 LKS, Wyred4Sound, Calyx Audio, AURALiC Vega, MSB, etc 有佢又未必一定好好聲, 不過加左佢又真係分析力高左, 但係會否又薄聲左, 音樂味少左?? 主流都係果粒Crystek cchd-575?  |
Esquire 正式會員158.xxx.xxx.187 |
2014-07-03 14:19 | |
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| [#2] Femto Clock 慢慢會成為DAC必要既東西 Esquire, 真正低 jitter 時, 分析力高左, 應同時更多的音樂感. 更加豐富飽滿. W4S 出Femto clock 版後的全部 客人order 都耍 Femto Clock 版. 因為價錢差不多, of course go la. 最後修改時間: 2014-07-03 22:48:01 |
odysseyhk 正式會員 1.xxx.xxx.198 |
2014-07-03 22:41 |
| [#3] Femto Clock 慢慢會成為DAC必要既東西 其實我唔太明白點解clock 嘅long term accuracy 會對聲音有影響，when sound quality relates more to short term accuracy.. |
welborne 正式會員 182.xxx.xxx.64 |
2014-07-03 22:49 |
| [#4] Femto Clock 慢慢會成為DAC必要既東西 Light Harmonics 之 Geek Series uses Crystek too. MSB is not using Crystek, it's another brand. Those in Calyx Femto dac are covered and sealed so we don't know their identity. |
CKKeung 正式會員 218.xxx.xxx.231 |
2014-07-03 22:49 |
| [#5] Femto Clock 慢慢會成為DAC必要既東西 還是通常改clock 或用啲珍貴嘅clock crystal 時都會順便俾份俾原本更穩定的psu佢，因此改善了jitter performance呢？ |
welborne 正式會員 182.xxx.xxx.64 |
2014-07-03 22:57 |
| [#6] Femto Clock 慢慢會成為DAC必要既東西 Crystek CCHD-575 or CCHD-957 are not femto second clocks. MSB Femto Galaxy is. You need to compare clocks at the same carrier freq at the same phase noise measurement offset. The real measurement is to measure offset at 1Hz, not 10Hz or 100Hz. MSB's 24.576MHz Femto clock does -99dBc/Hz @ 1Hz. My current custom clock does -85dBc/Hz @ 1Hz (same 24.576MHz carrier freq). CCHD-957 actually does -50dBc/Hz @ 1Hz. My custom clock is 35dBc quieter than the Crystek CCHD-957. And CCHD-957 is better than CCHD-575 by about 10dBc @ 10Hz. So CCHD-575 is nothing special, and while -957 is decent, most manufacturers do not know how to drive it properly yet. This is why the MSB Femto clock costs US$9950. Any Femto clock claims to be a few dollars more are not real femto second clock. Real femto second clock uses SC-cut crystals not AT-cut crystals. Also, a femto second clock needs to be shielded from air movement, better be temperature controlled and sealed inside a container. If you see the clock oscillator exposed to air, and they claimed it to be a femto second clock, then the manufacturer is lying to you. 最後修改時間: 2014-07-03 23:11:49 |
Kuro 正式會員 116.xxx.xxx.64 |
2014-07-03 22:58 |
| [#7] Femto Clock 慢慢會成為DAC必要既東西 ＞ 其實我唔太明白點解clock 嘅long term accuracy 會對聲音有影響，when sound quality relates more to short term accuracy.. Long term accuracy of clock has no effect to audio. But usually a clock that has long term accuracy has decent short term accuracy too. This is why many people went with atomic clock awhile back. But today, even the CCHD-957 has phase noise performance better than an atomic clock. ＞ 還是通常改clock 或用啲珍貴嘅clock crystal 時都會順便俾份俾原本更穩定的psu佢，因此改善了jitter performance呢？ Clock is very sensitive to power supply noise, especially high freq noise. So if you put a better power supply in a circuit with clock, the clock's jitter performance will improve with the better power supply. But to get to the biggest improvement, you still need a clock close to femto second performance and a very quiet power supply with very high noise rejection ratio. 最後修改時間: 2014-07-03 23:14:51 |
Kuro 正式會員 116.xxx.xxx.64 |
2014-07-03 23:02 |
| [#8] Femto Clock 慢慢會成為DAC必要既東西 re #6 Kuro 兄 good points! |
beeos 正式會員 1.xxx.xxx.203 |
2014-07-03 23:18 |
| [#9] Femto Clock 慢慢會成為DAC必要既東西 Kuro, Ok that makes some good sense to me too. |
welborne 正式會員 182.xxx.xxx.64 |
2014-07-03 23:50 |
| [#10] Femto Clock 慢慢會成為DAC必要既東西 Here is an article wriiten by iFi Audio (I guess its written by Thorsten Loesch) about Femto clocks, and Rubidium clocks. http://www.head-fi.org/t/711217/idsd-micro-crowd-design-hifi-man-he-6-takes-on-the-meaty-monster-page-82/645 Super Duper Features 1.4 Femto Clocks – Picky about Phase Noise Background All Femto clocks are good, very good in fact. They exhibit jitter levels lower than most clock crystals which leads to better sonics. An oft quoted benchmark for accuracy is Femtoseconds (Fs) / parts per million. Back in 2008, before the word “Femto Clock” became all the rage, AMR developed a special type of clock in DP-777 as part of the “Global Master Timing” (GMT) and “Jitter less” technologies (why special? See below, because not all Femto clocks are the same). We called it the GMT Clock platform (which is comprised of specialised hardware+software) as it is not just buying a “clock in a can” and job done. Having worked with all sorts of clocks, including discrete, Rubidium, Superclocks and not the least Femto clocks over the years, we know them quite well. All Femto Clocks exhibit excellent low phase-noise (measured jitter within the clock). However, as their origins lay in being part of SONET (http://en.wikipedia.org/wiki/Synchronous_optical_networking), the popular SONET targeted “Femto-clock” is less desirable as its best phase-noise performance is concentrated in the > 12KHz region (read: at the very top and way above the audible band, so benefits audio less). As an example, this link highlights the use of Femtoclock technology in the telecommunications sector where they are spec'd for: http://www.thinksmallcell.com/System/clock-frequency-accuracy-within-femtocells-for-timing-and-location.html The ubiquitous Femto (SONET) Clock This is an Optical Comm system (aka SONET - which is a Subset). We added the blue line to highlight the -70dBr region so that when referenced to the AP2 chart in the next section of the micro iDSD, it is more of an “apple to apple” comparison. The spike at 50KHz is the "signal" As you can see, for quite a few KHz around this region, phase noise is low, this is what matters in this application. However, the area around the green arrow is the most crucial human audible range of 20Hz > 20kHz where phase noise performance is less impressive in the region of -100dB to -70dB. Explanation Therefore, the key for AMR was to design a new system, the “GMT” clock platform which not only exhibits the lowest phase-noise in the crucial audible band, but offers precision (< 0.004ppm tolerance) adjustability with literally millions of possible frequencies (as per the DP-777 "GMT" Technical Paper). The GMT Clock system designed into the micro iDSD measures <280 Fs, comparable to many Femto-Clocks (because it was designed to give low jitter). From the AP2 graph of the micro iDSD below, you can see that jitter in 9kHz > 15 kHz is very good, the micro iDSD noise floor goes all the way down to -150dB which is virtually across the board.with no spikes. AMR/iFi GMT Clock Platform How this benefits the user Consistent, across the board negligible jitter means timing is supreme, with just the right amount of attack/decay and of course, tonal accuracy. We are really pleased with the very low jitter performance of the micro iDSD in the most crucial audible range – in fact, we would not mind if customers pit it against significantly more expensive DACs. We hope you found this interesting as it sheds some light on the particular attention we have paid to parts performance and custom design in the micro iDSD (actually, we took it from the DP-777!). |
welborne 正式會員 61.xxx.xxx.85 |
2014-07-04 04:02 |
| [#11] Femto Clock 慢慢會成為DAC必要既東西 Addendum: What about Rubidium Clocks? Below is a chart of several types of rubidium clocks. What they all exhibit is many sharp spikes in phase noise. Even though they measure well, some down to -150dB, when they spike, noise levels jump up to -70dB to -90dB. This is far from ideal which is why we have not used such clocks, neither in iFi nor AMR products. It all boils down to paying close attention to the specific clock/s used and its performance in the audible range. |
welborne 正式會員 61.xxx.xxx.85 |
2014-07-04 04:04 |
| [#12] Femto Clock 慢慢會成為DAC必要既東西 看來Rubidium clock 唔係好嘢嚟 |
welborne 正式會員 61.xxx.xxx.85 |
2014-07-04 04:18 |
| [#13] Femto Clock 慢慢會成為DAC必要既東西 ＞ Here is an article wriiten by iFi Audio (I guess its written by Thorsten Loesch) about Femto clocks, and Rubidium clocks. All that BS really means he hasn't really got a femto second clock as good as MSB or mine and try to justify his clock a femto second one by all that write up. For audio, clock jitter (phase noise) should be measured with the closest offset freq like 1Hz. He is saying that 150Hz offset is the most sensitive in human hearing. He is actually wrong. We can actually hear the jitter down to 1Hz offset. What that translates to would be far more micro details/micro transients, greater dynamics, far more deep low bass and far more vivid and live sound. Mid-range is also thicker as a result of this. 最後修改時間: 2014-07-04 11:03:55 |
Kuro 正式會員 116.xxx.xxx.64 |
2014-07-04 10:37 |
| [#14] Femto Clock 慢慢會成為DAC必要既東西 Femto Clock is not magic, a good DAC design end-to-end is key to audio performance. However, for the same design, using an improved clock with lower phase noise and jitter will have good incremental improvement. Not all Femto Clocks are equal indeed, low phase noise is key. And we can dig into low phase noise details. While the spec tell us a lot, how it translate to audio performance improvement could be complex may have dependency on other factors. What W4S told me is that they shortlist a few Femto clocks and conducted blind test to confirm which one to choose. It makes sense to me. 最後修改時間: 2014-07-04 10:56:50 |
odysseyhk 正式會員 1.xxx.xxx.198 |
2014-07-04 10:46 |
| [#15] Femto Clock 慢慢會成為DAC必要既東西 #13: agree that is a lot of sales pitch :) haha |
welborne 正式會員 61.xxx.xxx.85 |
2014-07-04 11:06 |
| [#16] Femto Clock 慢慢會成為DAC必要既東西 Same DAC design, change the clock to a real femto second you will have huge improvement, provided that you have an ultra low noise power supply for the clock. If you just attached an ultra low jitter clock to a conventional power supply, you get incremental improvements. A real femto second clock is the one measured by MSB, it starts with offset freq of 1Hz. RMS jitter is the area under the phase noise plot. I use the area from 1Hz to 1KHz offset. MSB also starts from 1Hz and they get 77 femto seconds RMS jitter. Anything higher than 1KHz from a good clock is insignificant, as you're just measuring the noise floor. Anything less is just a femto second clock wannabe. If you use a different offset measurement, even the Crystek CCHD-957 is a femto second clock. The problem is lack of standard of measurement. Crystek starts their measurement from 10Hz offset. Using Crystek's measurement standard, my clock has about 80 femto seconds. Where as the Crystek CCHD-957 has about 500 femto seconds (0.5 pico seconds). There aren't any real femto clock available commercially. It is because 99.99% of all clock crystals and crystal oscillators out there use AT-cut crystals. Real femto clock uses SC-cut crystals. You can custom order OCXOs from Morion in Russia. Good OCXO are femto clocks. It will cost you US$500 each for quantity of 1000. The one I used is bin sorted. One finds about one like that in a bin of 100. Don't expect to buy a clock commercially and expects it all to measure the same. |
Kuro 正式會員 116.xxx.xxx.64 |
2014-07-04 11:20 |
| [#17] Femto Clock 慢慢會成為DAC必要既東西 can anyone detail why compare femto clock vs 銣鐘? femto clock is a spec definifion where 銣鐘is true clock oscillation material. pls enligten me . |
er113 正式會員 202.xxx.xxx.90 |
2014-07-04 11:42 |
| [#18] Femto Clock 慢慢會成為DAC必要既東西 銣鐘 is atomic clock right? For audio, we need short term accuracy, not long term accuracy. Atomic clock is good for long term accuracy. For audio, the rising edge of the clock signal does not change from one cycle to the next, but the clock freq can drift over time. An atomic clock's freq does not drift over time, but from one rising clock edge to the next, it can change and it is far less accurate than a femto clock. Femto clock is pretty much the end of the line as far as clock is concerned for audio. There are limitations in physics how low phase noise can go. SC-cut x'tal is pretty much the bleeding edge as far a low jitter clock can go. |
Kuro 正式會員 116.xxx.xxx.64 |
2014-07-04 11:55 |
| [#19] Femto Clock 慢慢會成為DAC必要既東西 This one is very good in terms of clock jitter..  最後修改時間: 2014-07-04 14:00:58 |
Esquire 正式會員 158.xxx.xxx.187 |
2014-07-04 14:00 |
| [#20] Femto Clock 慢慢會成為DAC必要既東西 Btw, how important is clock in usb-spdif ddc device vs clock in DAC? |
welborne 正式會員 61.xxx.xxx.85 |
2014-07-04 14:01 |
