Reduce volume level

[truthz03]

Hi. I'm trying to use this soundcard inside my car. The problem is that my car has an fixed pre amplifier therefore the output from the audio injector is much too high.
Is it possible to reduce the output level per software?
Reducing the volume with the alsamixer is not the solution because there is some noise on the output which can't be reduced with the alsamixer.
This noise in combination with the pre amplifier in my car is about 50db loud

[flatmax]

Hi there,

Perhaps you can use a preamp before your amplifier ?
Next year we plan to reduce the noise out of the octo... a version 2.

Matt

[truthz03]

Thanks for your answer.
I now get a clear sound with an nf filter but there is a last problem.
While booting the raspberry pi there are many sounds like an old 56k modem.
Is it possible to disable the output while booting?
I'm using the rca breakout

Thanka
Thomas

[flatmax]

There is an output mute pin ... I wonder if your amplifier has a mute input ? If so, perhaps there is a way to send the correct mute signal to the amp ?

If you look at the RCA breakout schematic :
https://github.com/flatmax/AudioInjecto ... CA.sch.pdf

Pin 4 on the output header has a pin labeled "mutec" That is probably what you are after.

Matt

[truthz03]

Thanks for your answer. This is exactly what I'm searching for.
Yes my amplifier has an mute input because my application is an car multimedia system and the default connector (ISO connector) for this has an control pin for the car amplifier/antenna motor.
Now the only thing I have to do is to find out how to switch the 12V from my car with the 5V output of your soundcard

Thanks
Thomas

[robiwan]

There is an output mute pin ... I wonder if your amplifier has a mute input ? If so, perhaps there is a way to send the correct mute signal to the amp ?

It would perhaps be interesting to make a special breakout board that has relays (or two CD4066s) to short output to ground during mute ? Relays are nice for that true retro feeling