Rockbox Technical Forums

Support and General Use => Hardware => Topic started by: caesar on March 30, 2014, 03:07:53 AM

Title: iPod 5.5 Volume Control: How It Works
Post by: caesar on March 30, 2014, 03:07:53 AM

Hello!
I am interested in how does the volume control on iPod 5.5 (and other models) work?
Does it work in the digital domain or in the analog domain?
I am asking because I know that the firmware can separately adjust the volume through the headphones and through the line out (actually, Apple firmware sets line out volume to maximum, while Rockbox firmware sets the line out volume the same as headphones volume).

Title: Re: iPod 5.5 Volume Control: How It Works
Post by: saratoga on March 30, 2014, 03:14:50 AM

Quote from: caesar on March 30, 2014, 03:07:53 AM

I am interested in how does the volume control on iPod 5.5 (and other models) work?
Does it work in the digital domain or in the analog domain?

Analog.  Aside from a few rare devices, virtually all mp3 players use analog.  Digital works very poorly for this.

Quote from: caesar on March 30, 2014, 03:07:53 AM

I am asking because I know that the firmware can separately adjust the volume through the headphones and through the line out (actually, Apple firmware sets line out volume to maximum, while Rockbox firmware sets the line out volume the same as headphones volume).

IIRC line out should also be fixed like the Apple firmware, except at the lowest volume settings where there is no way to keep it fixed because it shares a mixer with the headphone output (Apple firmware just restricts volume range). 

Title: Re: iPod 5.5 Volume Control: How It Works
Post by: caesar on March 30, 2014, 03:39:27 AM

Quote from: saratoga on March 30, 2014, 03:14:50 AM

Analog.  Aside from a few rare devices, virtually all mp3 players use analog.  Digital works very poorly for this.

Didn't know this, thanks for clearing it out.
BTW do you know how it works on smartphones and PCs with integrated sound interface?

Quote from: saratoga on March 30, 2014, 03:14:50 AM

Quote from: caesar on March 30, 2014, 03:07:53 AM

I am asking because I know that the firmware can separately adjust the volume through the headphones and through the line out (actually, Apple firmware sets line out volume to maximum, while Rockbox firmware sets the line out volume the same as headphones volume).

IIRC line out should also be fixed like the Apple firmware, except at the lowest volume settings where there is no way to keep it fixed because it shares a mixer with the headphone output (Apple firmware just restricts volume range).

Didn't quite understand what exactly is the issue at the lowest volume.

Title: Re: iPod 5.5 Volume Control: How It Works
Post by: saratoga on March 30, 2014, 03:55:56 AM

Yes virtually all PCs and smart phones work the same way.

If the main volume is set too low then the line out volume is lowered too. The headphone and line out share one of several amps so they are not completely independent.

Title: Re: iPod 5.5 Volume Control: How It Works
Post by: caesar on March 30, 2014, 04:37:17 AM

Thank you for the info!