Currently, it is rare to find recent releases of cell phones that have an output for headphones (P2 or 3.5mm). This demise of the connection was strongly encouraged by Apple in 2016, when the company released the iPhone 7 and its first TWS headphones, the AirPods. From that moment on, devices that followed the same choice would prevent the user from using the cell phone’s audio circuit responsible for influencing the sound quality of the headphones.
Because the audio in your headphones is no longer dependent on your cell phone
Cell phones that do not have a headphone jack will not affect the audio quality of Bluetooth headphones. The reason for this is that the digital signal of the audio file is not converted to analog in the smartphone’s circuit, but in the wireless headphones. Bluetooth is a digital signal that is sent by the phone’s antenna to the Bluetooth receiver of an in-ear TWS or some other wireless type, which in turn has a DAC (Digital to Analog Converter) chip, responsible for converting the digital signal in analog.
Any headphone needs the signal sent to its speakers (drivers) to be analog. Hence the need for a DAC, but this chip alone will not be able to make the music play, as the analog signal needs to be amplified. That’s why we have in every music player device with at least one speaker a DAC and an amplifier, because when amplifying the signal converted by the DAC, the driver’s diaphragm will vibrate and produce the sound.
What if I connect a “USB headphone adapter” to my phone?
Unfortunately you will not use the cell phone’s audio circuit when connecting a “USB adapter for headphones” to your cell phone in the vast majority of cases, since today most of the “dongles” (portable USB DAC/amps) are not passive and yes active. This means that digital data passes through the USB port and is converted by an integrated circuit located inside the “USB headphone adapter”. Therefore, it is possible to connect a wired headset to these “adapters”, as the digital signal has already been converted to analog and amplified.
It is important to mention that there are two types of “USB adapter for headphones”. The “passive” and the “active”. On the passive side, the DAC/amp integrated in the cell board converts and amplifies the signal and sends it passively (without changes) from the USB connector to the 3.5mm connector. As for the asset, there is an integrated DAC and amplifier circuit that does all the work of processing the audio signal outside the smartphone circuit.
Where will I have more sound quality spending less?
To get better sound quality for less money, the best option is to use a “USB headphone adapter”, popularly called a “dongle”, which is actually a portable USB DAC/amp. The reason for this is that the cost of producing a Bluetooth headset is considerably higher than the value of a wired headset plus a “dongle” to connect to the cell phone. In an in-ear TWS, for example, we have a Bluetooth receiver/transmitter on each side to send and receive information from the smartphone, a battery, a DAC, an amplifier, several microphones and even a DSP processor, which will be responsible by handling the active noise cancellation (ANC) process.
In wired headphones, we usually have the speaker and a soldered cable. This will influence both the development, which will be focused only on audio quality, and the cost, which will be lower, because here we have fewer components compared to Bluetooth headphones. In addition, the output power of a “dongle” (portable USB DAC/amp) is usually considerably higher than that offered in notebooks, for example, allowing you to extract superior sound quality wherever you connect it.
