Add a bitcrusher. Reduce the sample rate drastically (down to 8kHz or 11kHz) rather than just lowering the bit depth. This mimics the low bandwidth of early digital speech chips. Step 3: Ring Modulation or Vocoding

It offers a classic, analog-style vocoder sound that can be pushed into the formant-shifting territory that Bitspeek excels at TAL-Vocoder.

The search for a ends with a few excellent freeware options that mimic its unique, retro robotic voice sound. Bitspeek by Sonic Charge is famous for its 1980s Speak & Spell toy effect. It uses a technology called Linear Prediction Coding (LPC) to turn normal human speech into a blocky, digital synth voice.

It’s primitive and "lo-fi" in the best way possible. It doesn't have a fancy GUI, but the sound is spot on for that robotic, hollow resonance. 4. Full Bucket Vocoder (FBVC)