No wire. Yet the song on your phone reaches your ear perfectly. Here’s every step of what actually happens. Your phone stores audio as digital numbers, around 44,100 samples per second. Sending all of that directly over Bluetooth would require too much bandwidth, so a codec like SBC, AAC or aptX compresses it first. It uses psychoacoustic techniques to remove sounds you can barely hear and sounds masked by louder ones, reducing the data while keeping the audio perceptually similar. Now the phone’s Bluetooth chip converts these compressed 0s and 1s into radio signals through modulation. The signal is transmitted around 2.4 GHz toward your earbuds. But WiFi and other devices use the same band, so interference is a problem. Bluetooth handles this using Frequency Hopping. It rapidly switches between different frequencies in a synchronized sequence. If one frequency has interference, the next hop can avoid it. The earbud receives the radio signal, decodes it back into 0s and 1s, and decompresses the audio back into digital numbers. But the speaker can’t work with numbers directly. It needs an analog voltage. That’s where the DAC, Digital to Analog Converter, comes in. It’s essentially the reverse of the ADC from the voice recording reel. The DAC converts those digital samples back into a continuously varying voltage. That voltage drives the speaker. A voice coil sits inside a magnetic field created by a permanent magnet. When current flows through the coil, electromagnetic forces move it back and forth. The attached diaphragm moves with it, pushing air and creating pressure waves that travel to your ear. Same physics as a microphone, but in reverse. The microphone converts sound into electricity. The speaker converts electricity back into sound. Codec. Modulation. Frequency hopping. DAC. Voice coil. Phone to ear. No wire.