Rational and clear information regarding audio equipment is not available today from mainstream audio literature. We only see unnecessary long treatises on high end audio, concentrating on technical descriptions and pointless analyzing of sound nuances, without any clear statements about the sounds fidelity.
Just like external sound cards, USB D/A converters are an integral part of computer audio systems and we would very much like to present our view of their performance. We are trying to avoid long descriptions by organizing USB converters into 3 classes, thus making the information about them simple and decisive. Placing all USB converters into only 3 groups may seem superficial, but after the following explanations the point shall be very clear:
CLASS 1 converters do not change the characteristic sound of acoustic instruments significantly. Trained or professional ears can easily determine the level of distortion caused by the digital to analogue conversion.
CLASS 2. The majority of USB D/A converters are members of this group. CLASS 2 converters lightly distort the analogue signal in a way usually referred to as “digital sound”. It is easily recognized in crescendo passages of orchestral music.
CLASS 3. Artificial sound, the annoying and unnatural timber of acoustic instruments, make the converters in this class completely useless for serious stereo systems. Although some modern music genres like techno-pop could even profit from distorted sound that the class 3 USB DAC can produce, music connoisseurs devoted to high fidelity should not be interested in digital mish-mash, produced from CLASS 3 converters.
That class 2 usb not always superiour to class 1.1 usb makes no sense to me Dalibor.
However, I can confirm that the SPDIF out of a Teralink X with an C-media usb 1.1 controller outperforms the usb input on my new NAD D1050 with XMOS. The difference is like day and night, with a more natural, open sound from Teralink X spdif and much less harsness. Less digital sound.
The question stands if we can improve the sound quality from usb 2.0 DAC devices by forcing a linux system to use usb 1.1 low speed protocol?
Only method I know to test this is to prevent the usb 2.0 ehci-hcd module from loading use the command: rmmod echi-hcd. The Ehci-hcd module is unfortunately compiled statically into the linux kernel of my current distro Ubuntu 14.04.
So talibor tell me if it Is possible to remove the ehci-hcd module on AP-Linux, I might give it a try.
This classification is very important, but how it can be determined in relation to specific DACs?
What defines this natural sound?
1. what characteristics (eg. Dynamic range, Resolution, Maximum sampling rate);
2. the processor type – which of known types of chipsets belong to 1, 2 or 3 class? (here are a few: ES9018, ES9016, ES9023, PCM5102, PCM2706, PCM2704, PCM1794A, AK4495, AK4490, AK4399, DSD1796, CS4398, WM8740 etc.)
Is it possible to install AP Linux on Compact Flash Card? If YES what size?
Does AP Linux support touch terminals? Is it possible to set portrait orientation instead of landscape?
I have TouchDiva Music streamer based on Celeron , 2GB RAM, 15″ touch display and 2*125W IcePower amplifier but boot device is only CF card.
Should I try to install AP linux on it?
Flash cards are bad and slow and it will ruin the sound of AP-Linux so it’s not recommended. Portrait is maybe possible. Check xrandr command on Linux. For touch display, I don’t know.
Yes, like any Linux you can boot it from SD, even if it’s not the best solution.
To avoid slow read problems from SD and potential slowdown/stuttering of sound playback you could preload the entire OS in RAM.
Unless it’s specifically forbidden from the motherboard you CAN boot from USB too.