3) Can you tell us about how you test finished designs, and about your reference system, along with your musical preferences?
Throughout my product design I measure and test components, modules & sub-assemblies. All finished products are tested for their specific functionality and battery functionality — charging is tested. Finally, listening tests for all products, are performed before shipping.
I found that with low noise, highly stable battery power to crucial areas of digital audio devices, (like USB receiver chips, low jitter clocks, D/A converter chips), great improvements in sound could be achieved but this wasn’t showing up in my measurements. For instance, early on while I was experimenting on the ESS DAC chip I found it sounded much better when run in synchronous clock mode rather than asynchronous mode where it used it’s inbuilt & well regarded ASRC (Asynchronous Sample Rate Converter). But nothing I could measure showed why this sounded better. And although I use an analogue 100Mhz scope & digital signal analyzer to aid in testing and fault-finding individual components, I remain committed to evaluating my designs using audition — by me, and by a local group of audiophiles in Ireland.
Just to say something about measurements here. I find noise which fluctuates because dynamic music signals are being processed is particularly difficult to measure. I haven’t yet discovered, or seen anybody describe, a technique for measuring this dynamically fluctuating noise.
For testing of DACs, I use headphones directly from the RCA outputs which gives me the best forensic insight into the sound. At other times, I use a Naska amplifier and some amplifiers of my own design outputting to Jordan JX92S fullrange speakers in speaker cabinet of DIY design — a 3D spiral horn design. My prototypes are also trialled in the local audiophile community who have a variety of audio equipment. Quad ESL 57s & 63s, Raidho & many other speakers; AirTight & a variety of solid state amplifiers and very heavily modified computers as source. DACs such as Lampizator, Meitner, Eximus and many others are used in auditions. We meet up via a local audio forum Tirnahifi
My music listening is varied, Swing Jazz, rock, some classical and some folk & country. Any music which I can connect to emotionally is my preference and I find good music systems make this far easier to achieve.
4) Can you explain, your view, how USB audio has evolved, issues that have been brought to light, and what the current state of the USB protocol for audio is?
USB audio came of age when Gordon Rankin introduced asynchronous USB protocol where the clock in the receiving audio device is the master clock timing the USB packets rather than the lower quality clock in the PC. This advance took USB audio out of the realm of an audio toy and into consideration for serious listening. It opened up computer audio to many and certainly began to appeal to audiophiles, particularly with the convenience offered by a music database, tagging and search functionality available.
There was great progress in USB audio and many subscribed to the belief that jitter was now under control with asynchronous USB and this meant the audio quality must be optimal. But many reported that their CD playback sounded more dynamic, alive and interesting — computer audio wasn’t matching this for some reason.
My path down the road of ultra low and stable power supply noise opened my mind to the psycho-acoustic repercussions of modulating noise. I had already premised that ultra low noise is one thing but stability of this noise is the more important characteristic. We can tolerate and even become unaware of noise which is stationary, not fluctuating — this is easily explained in ASA. Noise which modulates, irregularly, is much more intrusive in our auditory perception and captures our attention because it is not being treated as background.
The linked Youtube MP3 demonstration gives an example of this — what is happening here is that quantization noise is generated in MP3, but we cannot hear this fluctuating noise itself, we can only perceive it by its effect on the perceived blurring of the transients. I believe a more subtle form of this, low level noise, is at the heart of why digital audio can sound uninteresting, lacking in perceived dynamics, unmusical, unnatural. One major problem, in all this, is that measuring this low level fluctuating noise is a very difficult task & has not been fully resolved yet — glimpses are seen, however.
My audio devices, running directly from battery, do not suffer from this issue of delivering uninteresting audio playback, lacking in dynamics — it’s always been one of the main characteristics that users mention when they first hear my devices. Computer audio now matched and often surpassed even the best CD playback. From my discussion with a few customers in which we resolved why my audio devices weren’t providing the sound I know they can, I was reinforced in my conclusion that noise intrusion can deaden the sound, make it uninteresting to listen to, rob it of life. My direct battery power is addressing the main cause of fluctuating noise but it wasn’t until I heard the Intona USB isolator with my Ciúnas DAC that I could appreciate the audible effect of removing another source of noise coming from the USB connection itself.
I had already experimented with this, trying to block common mode (CM) noise using CM chokes on the USB signal lines — no effect; using ferrite rings on USB cable — dulling of sound; using a USB cable ferrous sheath covering — a significant reduction in hiss but some drop off in sparkle (this one will be revisited when time allows). But the USB isolation of the Intona affected the sound in a different way — it solidified the soundstage, made the interplay of the musicians more understandable, making the whole presentation more believable and musical. I knew this was a different type of improvement in sound and decided to investigate further and find a way to use USB isolation with and in my existing Ciúnas audio devices.
Again, in this case my premise is that the USB receiver chip is generating some self-noise within the chip & ultimately on the ground plane connected to this chip. This may be due to USB processing itself or, more likely, some overshoot/ringing on the very fast USB signal waveform (USB high speed 500pS is the rise time spec). I believe this is where the digital design requirements & analogue design requirements clash. A Reasonable amount of noise at the digital receiver does not cause bits to be misread but sensitive analogue circuitry like clocks are affected by ground plane noise. We can see a USB signal overshoot in the following measurement as the spikes at the top of the rising edge of USB waveforms in the plot (even though this is a plot of the slower full-speed USB & may be due to the scope probe used.
USB isolation of the USB signal lines removes any fluctuating noise, usually called common mode noise (CM noise), which is arriving at the USB receiver. Using a USB hub to regenerate the USB signals after this isolator is required to remove the jitter that all isolators add to the signal.
It took some time in testing, listening and ironing out the bugs but I eventually achieved success. My testing also revealed that USB reformatting/reclocking is needed after all isolation devices as they introduce jitter into the signal. My Battery powered ISO Hub was better sounding than the Intona when the group auditioned it side by side.
I recently released a number of products incorporating this technology:
ISO-HUB — a new device which offers 1 USB input and 4 isolated/reclocked high speed USB 2.0 outputs. Use before any USB audio device to obtain audible benefits of more sonic realism.
ISO-SPDIF — A world first — an isolated USB SPDIF converter. The Ciúnas USB SPDIF converter is integrated with the ISO-HUB technology providing a USB signal with optimal signal integrity to the USB/SPDIF converter.
ISO-DAC — Another world first — isolated USB DAC. The Ciúnas DAC again with integrated ISO-HUB providing an isolated and reclocked USB signal, internally, to the USB DAC.And lastly a product that many have been asking me to release, so they could avail of this battery power for non Ciúnas devices — a self-contained isolated battery supply which can be used to power many audio devices, not just my Ciúnas devices.
ISO-PS — an external battery power supply giving isolated, selectable voltages of 3.V and 6.V outputs and other voltages available on request
5) What do you for enjoyment when not designing digital audio devices and running your business?
I’m in the enviable position that one of my passions is actually my audio business. I believe most audio designers are similar and do this because of their passion and it’s no different in my case.
When I am forced to unplug my soldering iron and scope, I relax with painting. It’s similar to audio design in the way that one can get lost in doing a painting but it comes from a totally different part of the brain — the creative, intuitive part and yet the joy in a finished painting is similar to the joy in testing an intuitive design change & hearing the results.
Some paintings of mine…!