Raspberry Pi 3.5mm Audio Hiss

Issue

When using a Raspberry Pi 2 and or Raspberry Pi 3, the 3.5mm audio connector next to the HDMI port produces a noticeable static "hiss" when configured to output sound.

Solutions

Experimental Audio Driver

As of Feb 2016 there is a different audio method in the Pi firmware, set audio_pwm_mode=2 in /boot/config.txt to use it. This works for me.

HDMI-to-VGA Adapter

The whole reason I needed 3.5mm audio out was because I have a VGA monitor for this spare Pi setup. I just bought a HDMI-to-VGA adapter with 3.5mm audio out, this works perfectly similar to HDMI Audio Splitter above.

You need to add hdmi_drive=2 to /boot/config.txt when using one of these.

Things Which Did Not Work

Disable Audio Dither

Some people have said adding disable_audio_dither=1 to /boot/config.txt fixed this for them. Some people say this fixes it in RetroPie but not Raspbian. This did not fix it for me.

Other Solutions

Constantly Play Silence

Some people have had success making the audio device active but constantly playing silence with a command like:

aplay -t raw -r 48000 -c 2 -f S16_LE /dev/zero

HDMI Audio Splitter

A "HDMI Audio Splitter" or "HDMI Audio Extractor" is an inline HDMI-to-HDMI adaptor box with a 3.5mm audio socket on it. You would configure the Pi to output audio via HDMI, then plug the speaker or headphone into the 3.5mm socket on the splitter.

These often have other output like RCA and optical SPDIF. These also usually require a separate power supply, usually in the form of a MiniUSB cable (note: not MicroUSB like the Pi's power connector). I expect you could power it off one of the Pi's USB ports.

USB Soundcard

Cheap USB soundcards can be purchased off eBay for under $10, and professional-quality USB audio interfaces go up in price from there. Professional audio interfaces are often called a USB DAC (Digital-to-Analog Converter).

The Plugable USB Audio Adapter is said to be a good low-cost choice. The Audio Technica ATR2USB seems the cheapest professional option. I have a Behringer UCA222. Other popular brands are M-Audio, Lexicon, Roland, and PreSonus.

To set this as the default audio interface in RetroPie, run aplay -l to list audio interfaces. You'll see something like:

card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  ... other things here ...
card 1: Device [USB PnP Sound Device], device 0: USB Audio [USB Audio]
  ... other things here ...

So we can see card 0 is the built-in audio, and card 1 is the new audio interface.

Edit /etc/asound.conf and make it like the following, then reboot:

pcm.!default {
 type hw card 1
}
ctl.!default {
 type hw card 1
}

Root Cause

Unknown. Some people say this is a hardware problem, some say it's a firmware problem, some think it's a driver problem.

References:

• https://github.com/raspberrypi/firmware/issues/380
• https://delightlylinux.wordpress.com/2016/02/09/usb-audio-and-retropie-3-4-for-better-sound/
• http://raspberrypi.stackexchange.com/questions/19705/usb-card-as-my-default-audio-device/21989#21989
• https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=136445