Inline volume control for analog audio signals with push buttons [closed]

Question

I want to build something to control the amplitude of analog audio signals between the source (line level analog audio output already extracted and decoded from an HDMI source) and the AMPs. In addition, I want to use three push buttons (up, down, mute). I understand that such a circuit needs to be digital and needs to be active. I can provide it with a 5V or 12V DC. I am aware of the existence of digital pots. But it looks like they are usually controlled by an MCU, which is unnecessarily complicated for me. Any suggestions?

Thanks!

P.S. context: I'm trying to convert an old all-in-one computer into an external display with speakers. The reason I want a volume control is that Apple devices (Macs and iPhones) don't provide volume control over HDMI audio output. They don't support CEC. So I want to add the volume control before the AMPs. The machine has 3 physical volume control buttons that I can utilize. I have considered programming a microcontroller as an HID device with 3 keys, which is super easy, but 1. it's such an overkill, 2. it requires a USB connection. So, it's not ideal.

Answer 1

The audio sent over HDMI is usually embedded with a HDMI payload, sent as 'data islands' during the video blanking times. This audio could be PCM, or a compressed multichannel payload like AC-3 or DTS. On the face of it you need something more than just a simple digital volume control.

HDMI does have the "ARC" and "eARC" whose purpose are to route TV audio back to an AV receiver or soundbar. Then that AV device deals with volume control and other audio stuff instead of the TV. Maybe this is what you want?

Also note that most TVs and set-top-boxes have SPDIF or TOSLink optical. If you restrict the format to be PCM, then you need only to receive SPDIF, digitally modify the volume, then retransmit as SPDIF.

Otherwise, to pull out the HDMI audio, decode it, process it, then remultiplex it back to the HDMI requires basically the same capability as what a soundbar does.

Oh, and don't forget about HDCP: you need to be a licensee to obtain the keys to the HDMI kingdom to make that work at all. Unsurprisingly, HDMI doesn't make it easy to get access.

Answer 2

Just look for a digital potentiometer with up/down control and non-volatile wiper position storage (unless you don't mind defaulting to 50% on power-up). Two channels on one chip would probably simplify your design and ensure the channels don't get out of sync.