From Sound to Speaker: Microphones and Signal Chains

You sing into a microphone on stage. A fraction of a second later, the crowd hears your voice booming from enormous speakers. But what happened in between? Your voice is invisible air movement — so how does it travel through cables and electronics and come out the other side sounding like you? Think about this: your voice is made of pressure waves travelling through air, but cables carry electrons, not air. Something must translate between those two very different worlds. That translation is the heart of this lesson. Warm-up question below — have a go before reading on.

**What is a microphone?** A microphone is a transducer — a device that converts one form of energy into another. Specifically, it converts acoustic energy (sound waves in air) into electrical energy (a varying voltage in a wire). **Two main microphone types** *Dynamic microphones* work by electromagnetic induction. Inside the capsule, a thin plastic diaphragm is attached to a coil of wire suspended inside a magnetic field. When sound waves hit the diaphragm, it vibrates. The coil moves with it, and a moving coil inside a magnetic field generates a small alternating current — your audio signal. Dynamic mics are robust, need no external power, and handle loud sources well (drums, guitar amps). *Condenser microphones* work by electrostatics. Two electrically charged plates face each other — one fixed (the backplate) and one moveable (the diaphragm). Sound moves the diaphragm, changing the distance between the plates and therefore changing the capacitance, which produces a varying voltage. Condenser mics are more sensitive and accurate but require phantom power — usually +48 V supplied through the cable by the mixing desk or audio interface. **Microphone polar patterns** A polar pattern describes the directions from which a mic picks up sound. A cardioid pattern picks up mainly from the front and rejects sound from the rear, making it ideal for live vocals. Omnidirectional mics pick up equally from all directions. **The signal chain** Once the mic produces a signal, it travels through a chain of devices — each one performing a specific job: 1. **Microphone** → produces a weak mic-level signal (just a few millivolts). 2. **Preamp (preamplifier)** → boosts the mic-level signal up to line level (around 1 volt), strong enough for the rest of the equipment to work with cleanly. 3. **Audio interface or mixing desk** → converts the analogue electrical signal into digital data (analogue-to-digital conversion, or ADC) so a computer can process it; or routes multiple signals to different destinations on a live desk. 4. **DAW (Digital Audio Workstation)** → software (e.g. GarageBand, Logic, Ableton) that records, edits, and processes the digital audio. 5. **Digital-to-analogue converter (DAC)** → converts the digital audio back into an analogue electrical signal when you want to play it back. 6. **Amplifier** → boosts the signal to speaker level, powerful enough to drive speakers. 7. **Speaker (loudspeaker)** → another transducer; converts the electrical signal back into acoustic energy so you can hear it. Every link in this chain matters. A weak link — noise from a poor cable, a preamp that clips — degrades the signal for every stage that follows. Engineers say: 'garbage in, garbage out.'