Anyone interested even a little about the Raspberry Pi knows that it is, among many other things, a very useful tool for watching videos and listening to online or offline music. More and more people are installing on their RPI's operating system a music-player-software in order to play digital audio files.
Unfortunately, the built-in audio system of the RPI has poor sound quality (this is not a bad thing, if we think about the objectives of the RPI itself), so some other "equipment" is required to gain quality of audio: a Digital to Analog Converter, a board designed to convert the digital signal into an analog form.
There are a lot of RPI compatible DACs available on the market. The i2s DACs (i2s stands for Inter-IC Sound, Integrated Interchip Sound, or IIS) seem a god choice for RPI users, because of the kind of commutation interface. I'm not inclined to believe that a digital signal correctly copied across devices may suffer a loss of information. After all, in any uncompressed audio format, data are just 0s and 1s. Nonetheless, to the extent that DACs have to input all these binary numbers and output an analog voltage or current signal, their analog-side is very important for the quality of the sound, especially through headphones. The i2s interface allows a lower jitter (due to the separation between clock and serial data signals) and a shorter signal path (due to the direct connection to the RPI's GPIOs). The CPU usage reduction is also an element of evaluation.
Almost all audiophile-oriented distributions support a wide range of i2s budget DACs. The literature on the topic is endless, although pretty patchy. I will only refer to my personal listening experience with few of these add-on boards DACs in the same setup with the RPI2 as source.
Here are some of the best buys, classified according to their core converter chip.
PCM5121 - 32bit/384 Khz (limited by Linux kernel to 192kHz)
The chip is used by the JustBoom DAC Zero pHAT, which provides a headphones jack, a line out jack and an optional RCA stereo output (optional because is must be soldered). The JustBoom device is designed for the Raspberry Pi Zero, it's plug and play and has hardware volume control from
ES9023 SABRE - 24bit/192 kHz
This chip is supported by Volumio as Hifiberry+. There are three Audiophonics I-Sabre DAC versions (the V2 TCXO has even a stereo jack for headphones). Then there is the HiFimeDIY board: it lacks the phono out and is not even directly pluggable like a hat. Finally, we have the more audiophiliac Mamboberry version. Here too, the lack of a double stereo output (RCA and 3.5mm Jack) is a limit.
PCM5102 BURR BROWN - 24bit/192 kHz
There are several boards equipped with this chip: the Audiophonics or Picobber PiFi HiFi DAC version (they are identical, both with IR control for XBMC), the Hifiberry DAC+ version (without phone jack - you can solder it on the board, if you want to), the Durio Sound version and, last but not least, a SainSmart version. All of these DAC cards are supported by Volumio, RuneAudio, MoodeAudio, etc., and all have a phone jack output, but (this is a limit of the chip itself) no hardware volume control.
WM5102 WOLFSON - 24bit/192kHz
The only RPI-DAC provided with this chip (specifically designed for smartphones and tablets) is the Wolfson Audio Card. This card has a lot of useful features
- a 3.5mm jack for microphone input and two digital microphone modules
- two RCA electrical (not optical) connectors for S/PDIF receiver and transmitter (based on WM8804)
- two 3.5 mm jacks for analog stereo line: output for connection to stereo amplifiers or powered speakers and input for connection to smartphones or tablets
Nonetheless, apart from the lack of a pair of RCA analog connectors - as we find on equivalent cards - Wolfson's DAC biggest drawback is its poor compatibility with Linux operating systems. A different kernel and new modules are needed to run with the Raspian image. You can download the software for free here:
but it will be not plainly supported by our audiophile applications, even after the hacking.
PCM5122 BURR BROWN - 24bit/192 kHz
This chip is similar to the PCM5102 but with built-in hardware volume control. A Texas Instruments product as well. There is the Audiophonics and a Picobber PiFi HiFi DAC+ version (identical), the SainSmart version, the IQaudio Pi-DAC version and the JustBoom version. Note that all these DACs are able to get up to 32-bit/384 kHz but Linux audio drivers are limited to 192kHz.