A very blatant example of Amir's lies is in this post, in a thread since closed, providing no possibility to respond to this by parties involved or others:
The quote above can only mean one of two things or both:
1. Amir deliberately distorted and posted anything John Swenson said, which is very highly unethical behaviour (because John sure knows what async USB operates like).
or:
2. Amir doesn't know how async USB operates, which makes Amir highly incompetent.
It doesn't matter one bit how many projects Amir did at Microsoft or how many Unix books Amir wrote, the reality of his experience is that he's out of touch of Engineering, he was merely managing.
It appears several thousands of dollars of equipment, be they as good as AP, doesn't actually buy you competence in using this equipment properly. A few people have pointed out here and on other forums where technical knowledge is actually respected that he messed up his measurements greatly, thus casting doubts in the technically and scientifically less competent about products.
The continuing vendetta about some products and people shows a deliberate agenda.
Having worked a lot on my own system's USB Isolation (mostly related to power and not total galvanic isolation but a partial one using filtering) during December 2016, as well as on a DIY Linear Regulated Power Supply, there isn't a doubt in my mind, my listening sessions and the recordings of the DAC output and simple analyses and graphs made with Audacity and its generated 1K Sine that my system benefits from this approach. I listened first, only measured afterwards.
Of course YMMV (with time, more DAC manufacturers will probably start offering as add-ons or incorporating these tech into their products), so I'd recommend you give these products a try if not DIY inclined: at worse you can return them, at best you'll hear a USB DAC with a much better sound that you probably thought couldn't be improved especially in the cases of a direct connection of the main computer to the DAC (very high probability of that happening in this case).
I see jkeny also worked on his isolated products (and further is powering some crucial internals with batteries directly), iFi as well, there are others. Countless people will have the joys of getting better sound in their computer and external DAC rig now, even with quite expensive DACs as more research and tests are done.
Isolation on this side helps reduce some of the 'digititis' we can sometimes hear. Additionally, for having made the test for myself for a few days, this form of distortion is insidious: after having made my isolation circuits and the DIY Linear Regulated PSU and listening to these for a few days, I also removed them again. On initial listening, I could hear the lower sound quality immediately as the computer-generated internal noise as well the non-isolated nature of the normal USB connection (and Leakage Currents between the Computer SMPS and other PSUs did their damage).
However, and this is something I found quite troubling, after a couple of days, I seemed to have become acquainted to that lower-quality sound as well.
Of course, putting back the DIY isolated USB connector + DIY Linear Regulated PSU made everything much better again (far less distortion in the highest regions), and a lot of bass energy coming back, dark background and so on.
Now, at that point in December (I had decided to make it an Electronics month for the holidays), I was quite happy with the results, and it is at that point that I also put back to work my custom AC Filter Box.
Here, I wasn't expecting to have more results, because after all, I had in my mind, managed to isolate the computer-noise from the DAC using both these items: the custom isolated USB connector and the custom Linear Regulated PSU for the DAC.
I was surprised briefly that yet again here, I had quite a noticeable change in the dynamics, especially the bass energy. Plugged into this AC Filter box were my TV, my Blu-Ray player, my iMac (not my SET Amp which is on its own socket on a dedicated line).
These are all SMPS units... These all cause pollution of the mains additionally through higher Leakage Currents and their interactions with other PSUs (even, say your amp itself).
Now, John Swenson had described his thoughts on Leakage Currents quite extensively on Computer Audiophile, so it all made sense, so it can be worthwhile to search for his posts on them over there to get a good perspective on it. I also asked John at the time I chatted with him over at CA (something I am prone to do as he's one of the most knowledgeable EEs ever) whether it was possible to simulate this. Turns out that since these Leakage Current effects involve two or more PSUs, and the latter could potentially have several modes of operation, even that is a hard thing to do.
One more thing: I hadn't built the filter box for the video portion of my equipment, but I found out that I get much better picture quality putting the TV and the Blu-Ray player on the filter box too.
Long post, but to summarise: Isolation - give it a try, DIY or products, SMPS are the devil for audio (and video too), so avoid these at all costs. If you can't totally avoid them, use an AC Filter box in addition to the means of isolation because it is so easy to forget that an SMPS can cause issues via the mains too.
After this, I was planning to overhaul my recording home/project studio (USB Isolation and SMPS->Linear Regulated), and I still have work to do there, but fortunately, all my synths appear to already be Linear Regulated PSUs inside. Neat.
Goes without saying I have no affiliation with Uptone/Swenson/Crespi, jkeny, the iFi guys (although I do own an iFi iDSD Nano whose performance I seriously upgraded using my custom Linear Regulated PSU based partly on a Swenson design and my custom USB isolated connector and I like it far better that way!).
The quote above can only mean one of two things or both:
1. Amir deliberately distorted and posted anything John Swenson said, which is very highly unethical behaviour (because John sure knows what async USB operates like).
or:
2. Amir doesn't know how async USB operates, which makes Amir highly incompetent.
It doesn't matter one bit how many projects Amir did at Microsoft or how many Unix books Amir wrote, the reality of his experience is that he's out of touch of Engineering, he was merely managing.
It appears several thousands of dollars of equipment, be they as good as AP, doesn't actually buy you competence in using this equipment properly. A few people have pointed out here and on other forums where technical knowledge is actually respected that he messed up his measurements greatly, thus casting doubts in the technically and scientifically less competent about products.
The continuing vendetta about some products and people shows a deliberate agenda.
Having worked a lot on my own system's USB Isolation (mostly related to power and not total galvanic isolation but a partial one using filtering) during December 2016, as well as on a DIY Linear Regulated Power Supply, there isn't a doubt in my mind, my listening sessions and the recordings of the DAC output and simple analyses and graphs made with Audacity and its generated 1K Sine that my system benefits from this approach. I listened first, only measured afterwards.
Of course YMMV (with time, more DAC manufacturers will probably start offering as add-ons or incorporating these tech into their products), so I'd recommend you give these products a try if not DIY inclined: at worse you can return them, at best you'll hear a USB DAC with a much better sound that you probably thought couldn't be improved especially in the cases of a direct connection of the main computer to the DAC (very high probability of that happening in this case).
I see jkeny also worked on his isolated products (and further is powering some crucial internals with batteries directly), iFi as well, there are others. Countless people will have the joys of getting better sound in their computer and external DAC rig now, even with quite expensive DACs as more research and tests are done.
Isolation on this side helps reduce some of the 'digititis' we can sometimes hear. Additionally, for having made the test for myself for a few days, this form of distortion is insidious: after having made my isolation circuits and the DIY Linear Regulated PSU and listening to these for a few days, I also removed them again. On initial listening, I could hear the lower sound quality immediately as the computer-generated internal noise as well the non-isolated nature of the normal USB connection (and Leakage Currents between the Computer SMPS and other PSUs did their damage).
However, and this is something I found quite troubling, after a couple of days, I seemed to have become acquainted to that lower-quality sound as well.
Of course, putting back the DIY isolated USB connector + DIY Linear Regulated PSU made everything much better again (far less distortion in the highest regions), and a lot of bass energy coming back, dark background and so on.
Now, at that point in December (I had decided to make it an Electronics month for the holidays), I was quite happy with the results, and it is at that point that I also put back to work my custom AC Filter Box.
Here, I wasn't expecting to have more results, because after all, I had in my mind, managed to isolate the computer-noise from the DAC using both these items: the custom isolated USB connector and the custom Linear Regulated PSU for the DAC.
I was surprised briefly that yet again here, I had quite a noticeable change in the dynamics, especially the bass energy. Plugged into this AC Filter box were my TV, my Blu-Ray player, my iMac (not my SET Amp which is on its own socket on a dedicated line).
These are all SMPS units... These all cause pollution of the mains additionally through higher Leakage Currents and their interactions with other PSUs (even, say your amp itself).
Now, John Swenson had described his thoughts on Leakage Currents quite extensively on Computer Audiophile, so it all made sense, so it can be worthwhile to search for his posts on them over there to get a good perspective on it. I also asked John at the time I chatted with him over at CA (something I am prone to do as he's one of the most knowledgeable EEs ever) whether it was possible to simulate this. Turns out that since these Leakage Current effects involve two or more PSUs, and the latter could potentially have several modes of operation, even that is a hard thing to do.
One more thing: I hadn't built the filter box for the video portion of my equipment, but I found out that I get much better picture quality putting the TV and the Blu-Ray player on the filter box too.
Long post, but to summarise: Isolation - give it a try, DIY or products, SMPS are the devil for audio (and video too), so avoid these at all costs. If you can't totally avoid them, use an AC Filter box in addition to the means of isolation because it is so easy to forget that an SMPS can cause issues via the mains too.
After this, I was planning to overhaul my recording home/project studio (USB Isolation and SMPS->Linear Regulated), and I still have work to do there, but fortunately, all my synths appear to already be Linear Regulated PSUs inside. Neat.
Goes without saying I have no affiliation with Uptone/Swenson/Crespi, jkeny, the iFi guys (although I do own an iFi iDSD Nano whose performance I seriously upgraded using my custom Linear Regulated PSU based partly on a Swenson design and my custom USB isolated connector and I like it far better that way!).
