Digitial Audio

AJM

A friend of mine at work is searching for an answer on digital (optical) audio signals. I am not sure of his end goals but his interest is to be able to change the volume level of the output using the original source.

Basically, if using a device with digital audio output, he wants to be able to turn up the volume on the output device to increase the volume; not the amplifier receiving the digital signal.

Is there a protocol that encodes a bit pattern to instruct output volume levels for audio?

I haven't seen this ability on anything I have used but I know this is the right place to find out.

Agent420

Spdif is probably the most common.· I haven't done much with it on microcontrollers, but I note there is an Spdif Propeller Object in the Exchange.

As for increasing the volume, just like any digital value there are limits to how far the signal can be increased before it maxes out.·

AJM

Thanks for the help,

I guess I should try and explain a little better.

The question is whether there is a way to instruct the receiver to increase its output volume. He wants to know if this can be done over the digital signal. No need to increase the digital levels, just send a data stream to instruct the end unit to raise the volume.

RickB

That would depend on whether that device had been designed to respond in that manner. It's not an inherent quality of a digital input receiver.

Rick

AJM

I agree about the device being designed to respond that way Rick. However I have never seen a device that can even produce the signal

Agent420

If the device in question has remote capability such as IR, you can exploit that.

Failing that, you could always motorize the volume knob (really) ;-)

kwinn

The output of a digital audio device (CD, MP3 player, digital tuner, etc.) is usually a D/A converter of some type.

In some cases the output of a D/A can be changed by changing the reference voltage to it, but the range is limited.

The digital information going to the D/A can also be multiplied to vary levels, but again the range is limited.

Some devices use a digital pot between the output from the D/A (or preamp) and the amplifier to vary the level.

None of these methods would be easy to hack or control with an add on circuit.

With a bit more detail on the specific device and what he wants to accomplish he may get a better answer.

Agent420

^ As the OP mentioned optical, I'm fairly sure we're talking spdif rather than any adc analog output.· The volume level of the digital audio is managed by the internal dsp processing within the device...· Unless the device provides a remote method of control, the only ways to manipulate that signal are either creating an in-series dsp of your own (spdif in -> process data -> spdif out, can be tricky) or hack any user interface it provides (bypass volume up/down buttons or knobs).

dMajo

I have a self made carputer in my car. Because of the not superb quality of the analog audio outputs of the mini-ITX motherboard I wanted to go digital (spdif) to the audio amplifier and I faced the same problem. You can't control the volume throught the spdif signal, so I start thinking on how to tweak the amplifier to make this controls remote through the carputer gui until ... I found a very good quality amplifier with digital inputs and serial interface for all the parameters (volume, filters, subwoofer low-pass, balance, phase adjustments ...) management: car-theatre done !!! (and much more: navigation system, gps-sms security sistem, mp3 player, bluetooth hands-free for mobitel ...)