Smartphone as a DAP (Digital Audio Player): Is It Possible?

Using a smartphone with a 3.5 mm headphone jack to fulfill the role of a DAP (Digital Audio Player) is partially possible. Unfortunately, the experience is not the same due to differences related to features, external physical design, and optimizations in terms of internal hardware and software, including specific application and operating system functionalities.

What is a Digital Audio Player (DAP)?

A Digital Audio Player (DAP) is an electronic device specifically designed to play music in the form of audio files in formats such as MP3, WAV, FLAC, ALAC, among others. However, there are other characteristics that distinguish a DAP from other devices.

Physical characteristics of a DAP

Physically, a DAP usually has a smaller display (screen) than those found on smartphones, as there is no need for a large screen to view a music list or an album cover. In addition, the screen resolution is usually 720p or lower, resulting in lower power consumption.

Another physical characteristic found in DAPs is the presence of physical buttons that allow music control without the user needing to turn on the device’s screen to skip to the next track or pause playback. Some models also feature a knob [1] for volume adjustment.

DAPs include audio-oriented connections such as 3.5 mm and 4.4 mm outputs, which can be used to connect headphones, dedicated amplifiers, or DACs with optical and/or coaxial inputs. Some models also include an IIS (Inter-Integrated Sound) output.

[1] A knob is a rotary control, similar to a watch crown.

Internal hardware in DAPs

The internal hardware of a DAP is made up of several components, some of which are selected with audio playback performance in mind, such as capacitors and high-precision clocks. Manufacturers usually physically separate areas on the printed circuit boards (PCBs). These areas include:

• Power supply for components
• Pre-amplification and amplification (the area responsible for handling analog signals)
• Digital signal processing (DAC chips and related components)

This separation is necessary to prevent electromagnetic interference in the transmission of the audio signal.

Features in DAP operating systems (OS)

DAPs include several features in their operating systems to allow better control over audio playback. These include:

• Bitrate control for Bluetooth audio codecs: some DAPs offer the option to set a higher or lower bitrate for a Bluetooth codec, allowing greater transmission stability and lower battery consumption (for example, LDAC bitrate control on FiiO DAPs).
• Disable battery charging in USB DAC mode: some DAPs allow users to disable battery charging when connected to a computer or an external DAC.
• More volume steps: a higher number of volume steps makes it easier to finely adjust headphone volume to a more comfortable listening level.
• Gain levels: these provide finer adjustment of the device’s output power, enabling more precise volume control and making it easier to match headphones with different impedance and sensitivity.

Android OS optimizations in DAPs

Android-based DAPs do not run Google’s operating system in its standard form. Digital Audio Player manufacturers make changes to prevent interference in audio transmission that may be caused by the OS and by running installed applications.

Android in DAPs is modified so that:

1. The SRC (Sample Rate Conversion) [2] applied by Android’s audio APIs is bypassed.
2. There is no interference from other applications in the transmitted audio, allowing the music app in use to have exclusive access to the audio API.

These changes to Google’s OS allow bit-perfect transmission, a scenario in which there is no software-level interference along the audio signal path.

[2] SRC (Sample Rate Conversion) performs resampling, converting all audio files to a 48 kHz sampling rate.

Can smartphones with a headphone jack fulfill the role of a DAP?

Smartphones can partially fulfill the role of a DAP. To make this easier to understand, the characteristics of Digital Audio Players that a smartphone with a headphone jack can deliver are separated from those that are not possible for a phone.

DAP benefits that smartphones with a headphone jack can provide

If the user uses a smartphone with a headphone jack solely for music playback, it is possible to obtain the following benefits found in DAPs:

• Good-quality DAC chips: some smartphones use good-quality DAC chips.
• Non-shared battery usage: by uninstalling all non-music-related apps from the smartphone, better energy efficiency can be achieved.
• No distractions: enabling airplane mode and uninstalling messaging, email, and other non-audio-related apps prevents notifications from causing distractions.
• microSD card slot: some smartphones still have a microSD card slot, although this has become increasingly rare.

DAP characteristics that smartphones do not have

There are characteristics found in DAPs that smartphones with a headphone jack cannot provide. These include:

• Lack of physical music control buttons: without physical buttons, it is necessary to turn on the smartphone screen every time you want to skip to the next track or pause the music.
• Internal hardware is not optimized: there is no PCB design focused on protecting the audio signal from interference, nor are higher-quality components (capacitors and clocks) used to improve sound.
• Higher output power: over-ear headphones with lower sensitivity and higher impedance may prevent a smartphone from delivering good sound quality.
• Fewer connection options: it is not possible to use headphones with 4.4 mm balanced cables or to connect the smartphone via optical or coaxial cable to an external DAC.
• No audio-focused OS features: compared to DAPs, smartphones do not offer features aimed at better audio control, such as a higher number of volume steps or adjustable gain levels.
• No Android optimization for interference-free audio transmission: there is no bypass of the SRC applied by Android’s audio APIs.

Recommended related articles:
• The evolution of chipsets and Android optimization in DAPs
• How RAM memory consumption works in Android DAPs
• Why use a DAP (Digital Audio Player)?