How does ISO-Hub work with asynchronous USB?
USB sends data in packets, not a continuous flow. Inside the receiving device, the packet data is continually stored in a small buffer & converted to a continuous stream by using the local clock to time the data out of the buffer (it's this timing that is critical & the advantage that asynch provides - the timing out of this data is done from the clock in the audio device rather than a clock derived from the PC's USB packet stream).
Asynch tells the computer how much data to send in each USB packet in order to keep the buffer about half full.
All USB hubs do the same as the above - they are simply an intermediate station along the way between computer & final USB device
However, in this case, it is being used to receive USB packets & at the same time isolate/eliminate any noise on the data signal lines (D+ & D-) as well as the ground or 5V line - this is the isolation part. It also allows, by using ultra low noise & stable battery power, to provide a clean & optimally formed USB signal as output for transmission to the final USB audio device.
This is what an ISO-HUB does as a stand-alone device
That same technology is incorporated into my ISO-DAC & ISO-SPDIF thus avoiding the cables, different PS, etc. These are the first DACs & SPDIF converters that has incorporated such technology. Other DACs may say they have galvanic isolation but this is only a band aid partial solution as it doesn't isolate & clean the incoming USB signal - it isolates after the USB receiver - it's a case of the horse has already bolted.
Why are there 4 USB ports & how can they be used?
There are 4 USB ports on all ISO devices - ISO-HUB, ISO-DAC, ISO-SPDIF. Apart from the main function of the device (DAC or USB-SPDIF converter) there is an ISO-HUB built into all ISO devices. These USB ports are exactly the same as the ISO-HUB ports which provide isolated & reformatted USB signals.
Any USB audio device can be connected into any of the ports (except in the case of the ISO-DAC & ISO-SPDIF where the USB port on the right is used by the DAC or SPDIF function). Other USB devices may be USB devices holding music files, USB sticks or USB SSDs or HDDs. Playing back audio files from these storage devices plugged into the isolated & cleaned USB ports provides better sound quality than the same files on computer HDD, SSD or USB sticks.
For any plugged in USB devices that require 5V USB power this power can be injected into the rightmost USB port. See FAQ question "Is 5V power on the USB ports?"
Why is USB isolation needed - is battery power not low noise?
I once thought that battery power isolated my Ciunas audio devices from any electrical noise intrusion. I was wrong. When I tried the Intona, the first USB high speed isolator, I could hear a definite audible improvement. So the USB connection is another conduit for electrical noise intrusion.
Battery power breaks the ground loop pathway that often exists between computer & attached audio device which can be a conduit for electrical noise that affects sensitive audio devices.
Why is USB reforming needed after USB isolation ?
All isolation devices add timing variations in the signals being blocked - this is called jitter. USB jitter is audible & reforming/regeneration of the USB signal removes this jitter & results in better sound.
Is 5V power available on the 4 USB ports?
5V power can be injected into the rightmost USB port which then becomes available on the 3 other USB ports. This allows the user to control the quality & current capability of this power, 500mA, 1Amp, 2Amps. A USB cable for this power injection can be supplied.
Does this power injection introduce a 'dirty' ground into the output?
I have found that the major noise contributor affecting audio is the noise on the USB signal lines themselves, not the USB 5V or ground. What are the advantages of battery power?
Batteries are a stable, low noise source of power And aren’t sources of leakage currents or suffer from ground loops as mains rectified power can. This cuts out one source of electrical noise that can plague audio systems.
Some people state that batteries are noisy under load but this criticism is based on older sealed lead acid (SLA) battery technology where the chemical reaction needed to produce current is noisy. Modern battery technology, such as LiFePO4, which are used in all my products, is ultra silent under load..
What about the problem of battery charging?
The charging scheme uses isolated chargers which continually trickle charge the batteries. This allows the user to experience all the sonic benefits of batteries without any of the concerns about charging - it is plug & forget. There is no audible downside from this charging arrangement.
Are these batteries safe?
Unlike other Lithium Ion batteries these batteries use a different, stable formulation (Lithium Ferrous Phosphate, LiFePO4) which doesn't go on fire due to overcharging or shorting.
How do batteries compare to supercapacitors?
Supercapacitors are capable of delivering very high currents at low noise but they have some drawbacks. The main one is that they are found mostly in 2.5 voltage versions. To output 3.3V, two supercapacitors in series are required plus baancing circuitry & a voltage regulator needed on the output. Our experience is that balancing circuits & voltage regulators are inferior sounding compared to direct battery power.
What about the chemical noise of batteries?
Modern battery chemistry is far superior to lead acid (SLA) batteries where chemical reaction noise was an issue when a significant current was being drawn by the load. The design of these batteries use nano particles as anode which means that their reactive surface area is far greater than a lead plate in an SLA. This results in an internal impedance of 6mOhm (lower than almost all capacitors) which means an ability to deliver instant current of 120Amps pulse for 10 secs & 50Amp continuous output.
When supplying 3.3V at very low currents the load on the battery is minimal & one can safely say that there is immeasurable battery noise.
Old NIST paper (1995) on battery chemical noise - before LiFePO4 batteries were available & Ni-Cd is -205dB @ 10KHz
What noise is USB isolation blocking?
There are a number of different sources of noise on the USB connection - the 5V wire, the ground wire, both USB signal wires
The 5V USB power should never be used for powering sensitive audio devices - it just hasn’t got the stability or low noise requirements for this role - it’s has the opposite characteristics - variable quality, instability & noisy
The ground wire has similar variable quality & noise issues
Once the above two areas of noise have been dealt with (using battery power, for instance), the USB signal wires are the main source of noise intrusion. This is usually leakage current noise or common mode noise which the differential USB circuitry does not deal with.
What does this noise sound like?
It doesn’t sound of itself - it’s only it’s removal that is noticeable as greater dynamics, better insight into the interplay of the music - in two words more musicality & realism
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