ReplayGain

[Servatius]

(17-06-2016 21:42)simoncn Wrote:  I have always been doubtful about implementing this as a server-side feature. If the correct gain setting depends on whether the control point is using "shuffle (album)" mode or "shuffle (track)" mode, this implies that the control point (and possibly the renderer) need to be involved in selecting the correct gain setting.

So MinimServer may not be able to do anything useful at the moment for an existing combination of a control point and a renderer, but I am trying to find out what would be technically needed by a control point/renderer combination from the server in order to add a good ReplayGain support.

I am currently thinking

1. how the tasks of selecting the correct gain value (album or track) and applying it to the audio could be assigned to the control point and the renderer,
2. how the control point and/or renderer could communicate with the server to get access to the ReplayGain info stored in the original audio file.
   

For question 1, I see two possibilities:

• The control point decides according to an option or by shuffle mode between album and track gain. Then it accesses the ReplayGain info and computes the correct loudness level. Then it tells the renderer about the loudness level to use. (BubbleUPnP and UPnPlay have a feature to change the renderer's output level via UPnP, although it does not work with the Naim network player. The Naim app has two buttons for changing the output level. The information is passed via WiFi to the Naim network player which passes it on via a cable to the amplifier, causing the loudness knob to be turned. So its seems to be possible for the control point to change the renderer's output level, either via UPnP for renderers which support it or via a proprietary interface.)
• The control point decides according to an option or by shuffle mode between album and track gain. Then it passes the information which gain value to use to the renderer. (I don't know whether this can be done via UPnP, but the renderer's manufacturer could do so in their control point using a proprietary interface). The renderer then accesses the ReplayGain info and applies the gain value chosen by the control point before playing the audio stream.
  

Or shortly said, the control point decides between album and track gain, the renderer applies the gain value, but the question is whether the control point or the renderer retrieves the ReplayGain values stored in the audio file.

So for point 2 above I have some questions:

• Is it technically possible for a UPnP server to supply ReplayGain info to the control point when the latter is browsing the media tree?
• When the renderer plays the audio file, does it get the complete audio file including the ReplayGain info (provided that transcoding is not used) or does it only get the audio data? In the latter case, would it be technically possible to supply the ReplayGain info in a different way?
  

It is clear that as long as control points and renderers don't do such things nothing needs to be done in MinimServer. But owners of network players could ask the manufacturers for ReplayGain support. Manufacturers have a lot of (proprietary) possibilities for the control point/renderer combination. So if it were technically possible to access the ReplayGain info via UPnP, I would ask at the manufacturer of my equipment. It would be great if they could add a feature turning the amplifier's loudness knob according to the ReplayGain information. I mean, dreaming has often be the reason for innovation.