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Computer already have female audio jack used as audio output. I was shocked when I found devices like USB External sound card which we can insert it into USB port which is now acts as audio output. I always thought USB port only for data transfer and power transfer.

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    A USB port itself cannot be used as an audio port. You can connect a USB audio device like a headset for obvious reasons. Likewise a USB external audio card works by transfering digital audio data and converting it into an analog signal. – Ramhound Nov 8 '17 at 4:02
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    So, do you believe that music is not data?  What about text? – G-Man Says 'Reinstate Monica' Nov 8 '17 at 4:24
  • " I always thought USB port only for data transfer and power transfer." - for computers music is just the same kind of data as anything else (video, text, executable...). Its unclear what exactly your question here. USB sound card converts this information to audio signal. – Máté Juhász Nov 8 '17 at 5:31
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    @Ramhound, "A USB port itself cannot be used as an audio port." This is actually not true. Starting with mini and micro-USB, there are special extensions to USB connector that can turn the USB wires into plain analog audio channel (if supported). It is called "auxiliary mode", and is a part of OTG specifications, and is frequently used in automotive area. – Ale..chenski Nov 10 '17 at 4:19
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Pictured is a classic audio-class USB device. This is a digital audio device. It does have a high-quality D/A converter that converts digital data stream from USB channel into audio. It also usually has an input channel working in opposite direction, A/D converter into digital data stream, to support mike in a headset, or just a line input.

On a system level the initial state of drivers usually associates all audio streams with the on-board audio codec connected to back/front audio jacks. However, when a USB dongle of audio class is detected on a USB port, the system automatically re-assigns all audio streams (system sounds, music, video playback) to the USB dongle. When the dongle gets removed, the system redirects all sound back the default internal device.

It is a very convenient feature when main sound drivers are screwed: the USB audio drivers are fairly standard and robust, and the USB sound always works (in my experience), unlike various on-board proprietary audio codecs that frequently need special drivers that might be not always available or not supported any longer.

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Those are actually usb dongle soundcards.

  • please read my question clearly, I know I am not asking name of the device. – Jiggle Puff Nov 8 '17 at 4:46
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    Please read my answer again. The usb dongle contains D/A and A/D converters, which can convert sounds to binary and vice versa. sewelldirect.com/learning-center/what-is-external-sound-card It's the similar "problem" like a simple pci based soundcard - pci is not designed to act as audio output... So how it can do it anyway? It has a DAC chip on it and it can transfer data to/from motherboard and get power from motherboard. (Yes, you can't plug a jack directly on pci bus, nor usb port.) USB also can communicate with motherboard + got power. No magic. – Ipor Sircer Nov 8 '17 at 4:57
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    @IporSircer: I think your comment (which is very good) should really be part of the answer. – dirkt Nov 8 '17 at 6:11

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