I do not know for sure why it may be needed (after all, almost any music can be downloaded if it is about it), but users are interested in how to write what you hear in columns or headphones. Although some situations can be assumed - for example, the need to record voice communication with someone, sound in the game and similar things. The methods described below are suitable for Windows 10, 8 and Windows 7.
We use a stereo mixer to write sound from a computer
The standard way to write sound from the computer is to use a special "device" of your audio card recording - "stereo mixer" or "Stereo Mix", which is usually disabled by default.
To turn on the stereo mixer, right-click on the speaker icon in Windows notification panel and select the "Record Devices" menu item.
With a high probability, in the list of sound recording devices, you will find only the microphone (or a pair of microphones). Click on an empty place list with the right mouse button and click "Show Disabled Devices".
If, as a result of this, a stereo mixer will appear in the list (if there is nothing like that there, we read further and possibly use the second way), then you can also right-click on it and select "Enable", and after the device is turned on - "Use by default".
Now, any program for recording the sound using Windows system settings will record all sounds of your computer. It may be a standard sound recording program in Windows (or Voice Recorder in Windows 10), as well as any third-party program, one of which will be considered in the following example.
By the way, by installing a stereo mixer as a default recording device, you can use the Shazam application for Windows 10 and 8 (from the Windows Application Store to determine the song played on the computer.
Note: For some not the most standard sound cards (Realtek), another device for recording sound from a computer can be present instead of a "stereo mixer", for example, I have on Sound Blaster this "What U Hear".
Recording from a computer without a stereo mixer
On some laptops and sound boards, the "stereo mixer" device is either missing (or rather, not implemented in the drivers) or for some reason it is locked by the device manufacturer. In this case, there is still a way to record sound reproduced by a computer.
The free Audacity program will help (with the help of which, by the way, it is convenient to record sound and in cases where the stereo mixer is present).
Among the sound sources for recording Audacity supports a special Windows Wasapi digital interface. Moreover, when it is used, the recording occurs without converting an analog signal into digital, as in the case of stereo mixer.
To record sound from a computer using Audacity, select Windows Wasapi as a signal source, and in the second field - the sound source (microphone, sound card, HDMI). In my test, despite the fact that the program in Russian, the list of devices was displayed in the form of hieroglyphs, it was necessary to try at random, the second device was needed. Please note that if you encounter the same problem, then when you set the "blind" record from the microphone, the sound will still be recorded, but poorly and with a weak level. Those. If the recording quality is low, try the following device in the list.
Download the Audacity program you can free from the official site www.audacityteam.org
Another relatively simple and convenient entry option in the absence of a stereo mixer is the use of the Virtual Audio Cable driver.
Write the sound from a computer using NVIDIA
At one time, I wrote about the method of writing a computer screen with sound in NVIDIA ShadowPlay (for NVIDIA video card holders). The program allows you to record not only video from games, but also just video from the desktop with sound accompaniment.
This may also be recorded the sound "in the game", which in the case of enabled recording from the desktop, writes all the sounds played on the computer, as well as "in the game and from the microphone", which allows you to record the sound immediately and the sound and then What is pronounced to the microphone, i.e., for example, you can record a completely conversation in Skype.
How exactly the record is happening technically, I am not aware, but it works including where there is no "stereo mixer". The final file is obtained in the video format, but it is easy to extract sound as a separate file, almost all free video converters can convert video to MP3 or other sound files.
Read more: On the use of NVIDIA ShadowPlay to record the screen with sound.
I finish this article, and if something remains incomprehensible, ask. At the same time, it would be interesting to know: why do you need a sound recording from a computer?