[jtwrace]

PS: I can offer a set of jitter measurements on AP 2722 for one or two Offramp 5 converters with different options  as a contribution to the forum (provided interested party pays for shipping).

Heck yeah!  I'd love to see a full set of measurements on this dac.     Seems like a no brainer!

[kyrill]

with or without measurements the dac or in this case off ramp will not sound different.  In A/B against a contender (the Diverter) the measurements only  have some significance and then not even so* against the jitter measurements of the Diverter on the same measurement machine.

*Suppose A sounds better with equal  measurement outcome?
Suppose A sound worse with better measurement outcome?
Even when A sounds better with better measurement outcome it explains a floating logic as the above 2 outcome are equally possible as so ,many other non measured variables play their role in the complex gestalt

[audioengr]

with or without measurements the dac or in this case off ramp will not sound different.  In A/B against a contender (the Diverter) the measurements only  have some significance and then not even so* against the jitter measurements of the Diverter on the same measurement machine.

*Suppose A sounds better with equal  measurement outcome?
Suppose A sound worse with better measurement outcome?
Even when A sounds better with better measurement outcome it explains a floating logic as the above 2 outcome are equally possible as so ,many other non measured variables play their role in the complex gestalt

Good points.  Things that matter are:

1) does the measurement equipment terminate to 75 ohms well?

2) does the measurement equipment relate at all to a real-life system?  Does it actually emulate this?

3) what grounding and filtering is taking place in the measurement equipment?  Is it balanced, floating and not affected by the AC ground and ground-loops?

4) What ground-loops are created by the system equipment?  Are they the same with both converters?

There are probably more, and I agree that even a spectral plot is not that useful.  If there are lots of spikes in the plot, but the noise floor is lower, is that better sounding than lower spikes but a higher noise floor?  Who knows?

listening tests under like conditions are probably the best metric.
Steve N.

[audioengr]

Steve, we can schedule something up if you are still interested. I couldn't justify stealing vacation time from my family and weekends have been pretty busy. Remember we are not next door neighbors and it is a long drive for Steve.

PS: I can offer a set of jitter measurements on AP 2722 for one or two Offramp 5 converters with different options  as a contribution to the forum (provided interested party pays for shipping).

That would be interesting.  If my wife needs to go to Portland, which she does ocassionally, I'll try to set something up.  I would rather be there and even bring my own Mac Mini for listening-testing both converters.  Winter-time is a bitch for driveing though...

Steve N.

[tpaxadpom]

I had a chance to listen and measure Steve's latest version of Offramp 5 with external PSU and his new BNC coax cable. As promised here are some measurements done on Audio Precision 2722:
BNC
Jitter Peak
471.7ps 50Hz – 100kHz
377.3ps 120Hz – 100kHz
330.2ps 700Hz - 100kHz
330.2ps 1200Hz - 1000kHz
Average Jitter
237.2ps 50Hz – 100kHz
142.3ps 120Hz – 100kHz
94.88ps 700Hz - 100kHz
94.88ps 1200Hz - 1000kHz
Voltage
501.8mVpp (75 Ohm load)
994.4mVpp(high impedance load)
AES/EBU
330.2ps 50Hz – 100kHz
283ps 120Hz – 100kHz
235.8ps 700Hz - 100kHz
235.8ps 1200Hz - 1000kHz
Average Jitter
237.2ps 50Hz – 100kHz
142.3ps 120Hz – 100kHz
94.88ps 700Hz - 100kHz
94.88ps 1200Hz - 1000kHz
Voltage
2.4749 Vpp (75 Ohm load)
6.192 Vpp (high impedance load)

[kyrill]

thx for the measurement but how to give it meaning unless you can compare it with other contenders under exactly the same circumstances and the same measurement machine?

[audioengr]

thx for the measurement but how to give it meaning unless you can compare it with other contenders under exactly the same circumstances and the same measurement machine?

Even that is only mildly interesting as we don't really understand what is audible and what is not yet.  These measurements also don't describe how often the peak measurements are detected.  If it only happens once every 10 seconds, you definitely will not hear it.  When I look at the histograms, jitter peaks in the range of 300psec are not even visible because they occur so infrequently.  I can watch the measurements clicking and see the larger ones appear in the numbers every 10-20 seconds.

This is why my histograms are really more relevant IMO.

It would be interesting to hear the listening test feedback.  Which converter delivered more detail, better imaging etc..

Steve N.

[tpaxadpom]

Here is an FFT screenshot of Paul Hynes PSU (not loaded)

and here is one for Squeezebox Touch wall-wart also not loaded

generic 24V wall-wart not loaded

[jtwrace]

Great!  Do you have a loaded condition too?  Any other power supplies (Teddy Pardo etc) that you can share?

[tpaxadpom]

thx for the measurement but how to give it meaning unless you can compare it with other contenders under exactly the same circumstances and the same measurement machine?

Kyrill, it is a great point. The repeatability and reproducibility of measurements is quite high with AP2722. I've measured the same devices on different AP (jitter to be specific) and I haven't seen a huge discrepancy.  We are talking small numbers here tens of ps if that (not 100s of ps). In Stereophile John Atskinson provides jitter measurements using the same technique, so you can see how other devices score there.
Here are some pk jitter numbers for transporter and Touch using the same setup (different time):
Transporter:
AES/EBU 377.3-424.5 ps
SPDIF RCA 566 ps
SPDIF BNC 283-330.2 ps (rca cable with 2 bnc adapters yielded the same results)
Toslink 1.462 - 4.103 ns depending on the cable used. I've tested 4 or 5 different toslink cables.
Touch:
SPDIF RCA 377.3 - 324.5 ps
Toslink 1.604 ns

I don't believe these numbers can tell someone how the unit will sound. For instance Offramp 4 (basic version with wall-wart) produced very high jitter numbers but had similar sound character to Offramp 5. I no longer have Offramp 4 around to do A/B comparison so I cannot provide details on the differences. Going by the memory Offramp 5 with all upgrades is much more resolving.

[tpaxadpom]

Great!  Do you have a loaded condition too?  Any other power supplies (Teddy Pardo etc) that you can share?

No, I don't have other power supplies measured, but I can measure them if you want to send me one. I will return it back. The noise spectrum should be measured with psu loaded, but I didn't want to open the offramp as it doesn't belong to me.

[tpaxadpom]

Here is c/p of my e-mail to Steve, right after my auditioning:
As far as the sound goes. Offramp offers great low end extension, instruments are precisely placed in the space. The width and depth of soundstage is enormous. No fatigue over long term listening. It has a somewhat elevated low end or recessed mid/upper end. I can see why you preffer Mac mini to Macbook and your choise of SPDIF cable is also obvious. That semi rigid cable looked to me like 50Ohm RF cable I use to use for work but I haven't connected it to network analyzer to look at the impedance. I don't have AES/EBU cable and using generic XLR definitely affected the end result. So despite what measurements suggest I prefer the sound of SPDIF out.
As far as comparing it to Diverter HR. I've tried number of SPDIF, USB and power cables. Also Offramp favored ACME slvr cryo outlet vs Hubell. I have furutech GTX-D on power amps and Hubell on DAC. The best way to describe it is to use analogy. When I listen to Offramp 5 I am in recording studio. I can hear all instruments without being combined into sonic mess. I can easily follow each instrument, though Offramp seems to highlight leading instruments/voices. Diverter HR offers something that I have never heard with any other transport. It replaces speakers with music instruments. It offers acoustical density that is very close to real life performance. I need some time to analyze what I have heard to pick the right words. When I listen to Offramp I want to hold my breath to hear more details. With Diverter my feet start to tap with music.
I only tried 2 different power cords with Hynes PSU, I am sure more performance can be squeezed from Offramp. Also my speaker placement and component selection were voiced with Diverter HR, so this will contribute to the end result.

These comments apply to my initial setup, Offramp on the top of Paul's PSU with vibration control tweaks in place. Now after I've sent that e-mail to Steve I've tried relocating Offramp with PSU and USB short block. I've moved Diverter HR and Offramp setup to one shelf. The low end emphasis (darkness as some reported in other reviews) has completely vanished on Offramp. Steve's BNC cable seems to emphasize midrange and highs in my system, a bit too much for my taste though it makes a great combo with Offramp 5 depending on component placement.
I wanted to thank Steve for giving me the opportunity to audition this top notch converter.