Why fast Wifi makes sense even if have slow network.

I was thinking about, why my router with 300Mbit WiFi has 100Mbit Lan? Do it actually makes sense? After i visited my friends in a City (i live in an country), i found the answer.
The Wifi spectrum is really small. If all your neighbours  have WiFi, then most channels are used 2 or 3 times. In this case, using high speed WiFi devices makes lots of sense.
This image should help to understand it:

4€ usb audio adapter, is it real?

I found a 4€ usb audio adapter on ebay. Lets take a try and see what can it do.

Usb id: 0c76:1607 JMTek, LLC. audio controller

dmesg:

[19664.343331] usb 1-4.2: new full-speed USB device number 9 using ehci-pci
[19664.417955] usb 1-4.2: New USB device found, idVendor=0c76, idProduct=1607
[19664.417958] usb 1-4.2: New USB device strings: Mfr=0, Product=1, SerialNumber=0
[19664.417961] usb 1-4.2: Product: USB Headphone Set
[19664.420557] ALSA mixer.c:929 51:0: cannot get min/max values for control 2 (id 51)
[19664.420599] ALSA mixer.c:929 49:0: cannot get min/max values for control 2 (id 49)
[19664.420637] ALSA mixer.c:929 50:0: cannot get min/max values for control 2 (id 50)
[19664.425185] ALSA mixer.c:929 51:0: cannot get min/max values for control 2 (id 51)
[19664.425207] ALSA mixer.c:929 50:0: cannot get min/max values for control 2 (id 50)
[19664.425247] ALSA mixer.c:929 49:0: cannot get min/max values for control 2 (id 49)
[19664.428091] input: USB Headphone Set as /devices/pci0000:00/0000:00:1a.7/usb1/1-4/1-4.2/1-4.2:1.3/input/input17
[19664.432635] hid-generic 0003:0C76:1607.0007: input,hidraw3: USB HID v1.00 Device [USB Headphone Set] on usb-0000:00:1a.7-4.2/input3

Now let's take a look insight:

Every thing works out of the box. But how about quality? Here are some images of simple sinus signal:

 This is 400 Hz signal generated with gstreamer. Small drop are probably result of resampler in pulseaudio. But we can see that there is more than just 400 Hz. Behind of it there is high frequenzy noise outside of hearing spectrum.

Here is one more sample with 20 000 Hz. Similar result. It is not perfect, but it is still usable.
So, if you need some device with better quality, you should try some one from higer price class ;)