A vocoder, or "voice encoder," is a tool that analyzes and synthesizes human speech. It functions by dividing an audio signal into various frequency bands and modulating them with a different audio signal, known as the "carrier." The tal vocoder follows this principle:

1. Input Signals: It requires two input signals: the "analysis" signal (usually a human voice) and the "carrier" signal (any audio signal).
2. Analysis: The analysis signal is passed through bandpass filters, dividing it into multiple frequency bands, and extracting envelopes representing the energy level of each band.
3. Modulation: The carrier signal's frequency content is modified by the envelopes extracted from the analysis signal, creating a synthesized sound with the spectral characteristics of the carrier signal and the dynamic characteristics of the analysis signal.
4. Synthesis: The modulated signals are recombined to create the final output signal, which has the tonal qualities of the carrier signal and the rhythmic and intonational patterns of the analysis signal.
5. Additional Processing: Tal vocoders often include extra processing stages, like noise gating, compression, and equalization, to improve the output signal's quality.

In short, a tal vocoder analyzes an audio signal into frequency bands, modulates a carrier signal with the extracted envelopes, and recombines the modulated signals to create a unique, expressive sound that combines the characteristics of two different audio sources.

The Best vocoders are below (all free)

1. TAL Vocoder: TAL Vocoder is a highly-regarded free vocoder plugin, known for its high-quality sound and user-friendly interface. It offers various parameters to tweak, such as the number of bands, carrier signal, and noise gate settings, allowing for precise control over the vocoding process. Its versatility and sound quality make it a top choice for many musicians and sound designers.
2. Audacity Vocoder: Audacity, a popular open-source audio editor, includes a built-in vocoder effect. While it may not be as feature-rich as some standalone vocoders, its accessibility and ease of use make it a great starting point for those new to vocoding.
3. Xfer Records Vocoder: Xfer Records, the creators of the popular Serum synthesizer, offer a free vocoder plugin. This vocoder provides a wide range of customization options, including adjustable band count, carrier signal selection, and built-in effects like reverb and delay. Its intuitive design and high-quality sound make it a strong contender in the free vocoder market.
4. Voxengo Voxformer: Voxengo Voxformer is a versatile vocal processing plugin that includes a vocoder function. While not exclusively a vocoder, its vocoding capabilities are impressive, offering adjustable band count, carrier signal selection, and various vocal processing tools like compression, equalization, and de-essing.
5. GVST GVocoder: GVST GVocoder is a lightweight, easy-to-use vocoder plugin that delivers solid results. It features adjustable band count, carrier signal selection, and a simple interface, making it an excellent option for those looking for a straightforward vocoder solution.

To use a vocoder, you typically speak or sing into it. A vocoder analyzes the audio signal from your voice, breaking it down into various frequency bands. Simultaneously, a carrier signal, which can be a synthesizer or another audio source, is also fed into the vocoder.

The vocoder then applies the amplitude envelope of your voice to the carrier signal, creating a synthesized sound that combines the tonal qualities of the carrier signal with the rhythmic and intonational patterns of your voice. This process allows for the creation of unique and expressive sounds, making vocoders popular in music production, especially in electronic, pop, and hip-hop genres.

In summary, you can both sing and speak into a vocoder, as it processes and synthesizes the audio signal from your voice.