Manufacturer's Comment

Steven, thanks so much for your thorough review of our LightSpeed USB cable. Having created reference-class DACs in our Da Vinci DAC and Da Vinci Dual DAC, we quickly discovered that their performance was both limited and compromised by existing USB cables, just as you found, when playing higher-resolution music files such as DxD (24/352.8K) or DSD 64/128.

The main issues we encountered were those of feedback endpoint transmission and turnaround, as eloquently described by our respected colleague, Gordon Rankin.

We are often asked why we designed LightSpeed to have a bandwidth of 10 Gigabits/second, when the transfer rate specified by USB 2.0 is only 480 Mbps. The USB 2.0 standard is a big umbrella, with a number of different sub-classes. The exact protocols used for USB 2.0 hard drives, printer or other peripherals are different than those used for music transmission-- USB Audio Class 2.0--especially when asynchronous transmission is involved. Unlike USB interfacing between a computer and printer, digital audio signals stream in real time. If a printer misses part of a signal, it can and will ask the computer to send the signal over and over again, until it gets it right. That's not an option in streaming an audio signal to a DAC; if the DAC misses part of the signal due to noise or jitter, it's forced to "guess" at the missing bits. When that happens, you no longer have bit-perfect digital audio; besides which, if the timing of an arriving music signal package is altered, there is no way to correct it again.

LightSpeed's extreme bandwidth provides the equivalent of a 20-lane highway for the digital audio signal, so that any possible traffic "jam" or noise, such as the clicks you heard from other USB cables, simply won't happen. LightSpeed is designed for highest speed transmission, so that even if it is used with the USB 3.0 protocol in the future, the cable's transmission capabilities will still be quite sufficient.

You've perfectly described the performance benefits that result from LightSpeed's ability to provide a noise-free, bit-perfect signal: " an enormous soundstage", "low background noise", " fast with no overhang", " dynamic qualities are first rate", "bass moved the walls and rattled the windows in my room", and so on.

We are especially pleased by your statement, "Its special qualities of speed, detail, soundstage and ambience reproduction, along with its low noise capabilities, place it among the finest USB cables I have yet heard", and note that the only USB cable you felt was comparable to LightSpeed (and then only in some areas) costs $3490 for a 1-meter cable with power supply. It is gratifying for our hard work is appreciated, and we promise to continue to design and offer products that push the envelope of what is possible in audio reproduction.

Finally: thanks and congratulations to Editor Michael Lavorgna for having developed AudioStream into one of the leading news sources in the world of digital audio. We wish you many years of growth and continued success!—Larry Ho, Gavin Fish, Kim Kaplan, Bill Leebens // Light Harmonic


bsm's picture

Also, it'd be great if Light Harmonic could actually provide their test data showing other cables not reaching the 2.0 standard, as well as data showing dropped bits in others vs. no dropped bits in theirs.

Archimago's picture

Yeah, wish these companies would back up their claims.

Stereo DSD128 and 24/352 isn't exactly a lot of bytes/s for a decent USB2 cable to transfer (compared to say a hard drive)...  I have not run into any pops/crackles/etc. with JRiver and the TEAC DAC at these speeds with generic USB cables.

I would submit that some of the issue may be JPlay and how it influences the CPU load. For some reason audiophiles like to also limit the buffer size to bare minimum on JPlay which of course exacerbates the problems.

Steven Plaskin's picture

I found issues with some cables using just JRiver (DoP) and OSX with Audirvana Plus.

JPlay didn't seem to make a difference. I also thought that the buffer might be an issue with JPlay, but increasing the buffer didn't solve the problem.

24bitbob's picture

Another fascinating review, thanks, but wow, $1,000 for a USB cable. 

How about this from the antipodes:  cables that also separate the power from the signal.  Not inexpensive either but closer to the 'do-able' range for more people


Wavelength's picture


If a printer misses part of a signal, it can and will ask the computer to send the signal over and over again, until it gets it right. That's not an option in streaming an audio signal to a DAC; if the DAC misses part of the signal due to noise or jitter, it's forced to "guess" at the missing bits. When that happens, you no longer have bit-perfect digital audio; besides which, if the timing of an arriving music signal package is altered, there is no way to correct it again.

While it is true that isosynchronous data sent from the computer to the DAC does not have error correction. I have set up a pretty elaborate test setup for cables and in my experience there has been obvious data errors because of this but not consistent errors. Also the DAC when it does receive a packet error does nothing to the data it receives and in most cases is only a BIT off and playback is not totally compromised.

From above... let me explain further what Asynchronous USB Class protocol is all about. This will help you understand what causes pops and clicks.

Basic USB... when the computer sends data out it's port it sends an OUT request which tells who it's going to and then it sends the data. When the computer wants a device to send data it sends an IN request with the address of the device and at that time the computer stops sending data opens the line for the device to send data to the computer. This was originally conceived as a poll and select protocol.

Now with Asynchronous USB enumerates (tells the computer what it is) two different endpoints. Each device can have 7 in and out endpoints, with endpoint 0 in/out being the control point for all devices. The two ASYNC endpoints are the input or data stream from the computer and the feedback stream which tells the computer to slow down or speed up the data stream so the dac chip does not run out of data. The 3 byte feedback pipe to the computer happens about every 32 packets of data.

So the big reason for pops and clicks is not the receiving of bad data. It's basically that the computer is not doing flow control correctly. Think about it this way... if you initiate cruise control on your car and you hit a hill and the car slows down then really there is no control. The same way with ASYNCH protocol if you need more data or less data then the device controller (at the dac chip end) has nothing to do but reset it's buffering system. This is what causes pops and clicks, not bad data.



Steven Plaskin's picture

Thanks for the excellent explanation Gordon.

Priaptor's picture


I am not sure if you received a "broken in" cable or not, but my first impressions were that "this cable sucks".  I have been fooled enough to give it some burn in time.  Lo and behold, by day 3 of constant usage, no doubt I realized my initial impressions were way too hasty.  I can say from a  resolution standpoint, this cable resolves like none I have ever used.  

Unfortunately (or fortunately) I had to leave for a vacation so I only had day 4 after burn in for my initial assessment but really like the direction the cable was going, however, I still haven't realized the soundstage of my current standard.  Just an early assessment and I fully expect the cable to continue to improve with time in all aspects.

While I have experienced "burn in" differences with other cables, as I am sure most of us have, I have never experienced such a difference with a cable as the Light Harmonics.  If the soundstaging improves as I fully expect it to and for sure hope it will, I can see this becoming my new reference-BUT, it is not there just for me.   

Steven Plaskin's picture

Yes, the cable needs a good deal of break-in. At first I thought the soundstage was a bit small and the bass lacking. It does get better with play; much better.

For DACs like your MSB Tech DAC IV Diamond plus, it will sound very good. It loves a truly neutral DAC.

Priaptor's picture

BUT this was quite a surprise as to how much character change I noticed after 3 days. 

I am looking forward to getting some more hours on it.  I really like what is was starting to do.

Jason Victor Serinus's picture

I initially tried this cable cold, and was extremely disappointed. After I read this exhaustive and extremely positive review, I contacted Bill Leebens, who is repping Light Harmonic. He informs me that the cable needs two weeks of solid break-in to fully come into its own. Alas, mine is in a box in a pod somewhere, staying warm until we sell our house and begin to settle into another. Given Steven's endorsement, I'm kicking myself for not leaving it out. I could have set my laptop on repeat and broken it in by now...

Larry Ho's picture

Jason, Glad to see your message here...

Proper break-in procedure in my mind, I know you want to make the period shorter if possible. Right? 

1. For ultra high speed differential pair 

Maybe the quickest and easiest way to break in Light Speed is to use it between USB 2.0 external Hard Drive (better larger volume and fast one)... Continously copy big video files back and forth. Random 0 and 1 and constantly high speed at 480M Hz shall break-in this part faster.  

I saw one article somewhere, one programmer even wrote a simple program for this. Copy files in both directions. Up stream and down stream... ;-)

2. Power leg part of LightSpeed

Use Da Vinci to break-in the power legs part of Light Speed is not agood idea, because it's SELF-Powered. Better use some DAC or some devices that will draw near 300mA ~ 400mA constantly...

I think by using above method, LightSpeed USB will break-in faster.

Sorry that like Da Vinci, I choose the best material and construciton method for LightSpeed and God is fair. It usually needs more time....


bsm's picture

I'm curious as to how "burn in" changes the bits.

Priaptor's picture

I was as baffled as you.  I have never had a cable with such drastic changes in the burn in process.  I was ready to bring it back from where it came after the first night.   It literally "sucked" so bad, I emailed several people with my initial impressions figuring there was no way for the cable to deliver based on my initial impressions, what the claims by the company was.

Well after 3 days, the character totally changed for the better.  I am looking forward to more sessions when I get back as this cable has me baffled.  I have never seen such dramatic changes in character in any cable I have ever used. 

Steven Plaskin's picture

Hi bsm.


While I'm hardly an expert on cable design, I have found that many USB cables I have listened to improve with use.

The 5 volt line insulation, the insulation for the signal, timing changes with insulation forming might influence the sound even if the bits are not changed.

This is an interesting link from Cardas cables:


This AudioStream discussion might also add some insight to your question:

billleebens's picture

We are investigating ways of breaking-in or burning-in the cables before shipment. 
No conclusions at this point.

Right now we have our hands full with the Kickstarter campaign for our next product, "GEEK", which is a dongle-style DAC/headphone amp that handles up to 384k in PCM, and is DSD-capable.

Lana Sander's picture

Since I can't measure the cable, I don't know. But Light Harmonic does make some really excellent sounding gear. The Da Vinci DAC was one of the best DACs I have ever lived with. 

reverendo's picture

is there any subjective comparison to the three other USB cables you mentioned in the beginning of your review. I know all three of them well and the AQ Diamond fit my system best. Am burning in a Purist Ultimate at the moment, but might be able to compare the Diamond, the Ultimate and the Lightspeed to each other.

Best regards


highstream's picture

While the Lightspeed is undoubtedly a fine cable, I agree with reverendo and find this review less than forthcoming. The author has a plethora of top quality cables on hand and doesn't mention any specific comparisons?? Was that because there wasn't enough time, or...? Each cable has its own presentation style and characteristics, just as each system is different and has its own characteristics and needs. Without some comparison, there's no way to place the Lightspeed cable sonically. "...speed, detail, soundstage and ambience reproduction, along with its low noise capabilities" doesn't really tell the reader very much.

wfojas's picture

All the cables used in the USB comparison (the Audioquest Diamond, Synergistic Research Active SE cable and the Wireworld platinum) as well as the Synergistic Research Galileo Cables seem to compare so well with this, how is this not a Greatest Bit? Just curious as to what keeps it out.