A turntable is the only way to decode the grooves of LPs into audio. USB turntables made for this purpose have emerged as a new product, and you can still use traditional turntables with adapters to connect to your sound card. Consistent platter speed and vibration isolation are important regardless of design. Look for heavy, well-built units, and place them on a level surface free of vibration, which can transfer as low frequency hum.
The Recording Industry Association of America (RIAA) developed a standard for bass and treble equalization to assure LP groove width remained consistent. Frequencies are adjusted during the cutting of the record, then adjusted back by stereo amplifiers with "PHONO" settings. Without this playback equalization, LPs will sound thin with no deep bass. Account for this equalization either through an amplifier or a software feature for USB turntables.
You'll need software for processing digital audio to format your music. Steps you might take include breaking an LP side down into individual songs and using digital signal processing (DSP) to remove noise artifacts typical of the turntable/LP system. Many digital audio editing packages will provide these features and may come with the purchase of a USB turntable. Free, open-source software programs include Audacity (see link in Resources section).
The LP and turntable are components of an electromechanical reproduction system and therefore require adjustments for best performance and sound. Stylus weight and tone arm anti-skating force can affect sound quality. Refer to your turntable's manual for recommended settings and maintenance. Use a solid surface free of vibration and heavy enough to absorb noise created by footsteps near the turntable. If your turntable has a ground wire, connecting it to a chassis point on an amplifier or computer case may eliminate electrical hum.