An emulator author since the 1990s, CLK is my current thing. It's a subcycle-accurate emulator of an ever-growing roster of machines which focuses on latency elimination and applying proper signals processing: depending on the platform, of course, audio is normatively sampled internally in megahertz and sampled down to your computer's rate, and video is presented via an emulation of a CRT, complete with real implementations of sync handling, composite decoding and phosphor decay.
Both are linked to the host computer's hardware.
- if you have a 120Hz or 144Hz gaming monitor, you will see 120 or 144 independent frames a second, just as if you pointed a 120fps or 144fps camera at a regular TV screen. This makes CLK the lowest-latency emulator available if you're willing to purchase appropriate hardware: video latency on a 144Hz monitor is 1/144th of a second.
- if you have a 96Khz or 192Khz audio output, you will hear 96k or 192k independent samples a second, just as if you were really recording the real machine.
Genuine composite video generation and decoding produces a genuine emulation of a composite display, including all proper artefacts and synchronisation issues if the emulated machine is capable of causing them. This emulator has accurate video through running an accurate video pipeline. No subjective effects or post-processing is applied.
The emulator also emphasises ease of use. From any inserted piece of media it will automatically determine the target machine and its proper configuration, then load and launch the inserted game. It uses a combination of static and dynamic analysis to achieve that goal.