Volume control in Dock mode

[UKenGB]

By which I mean, use the iPhone's volume controls (on-screen or buttons) when connected to a dock whose audio out is connected to an amplifier of some sort. If playing music and placed into a connected dock, the iPhone switches output from its own internal speaker (or the headphone port) to the Dock connector and hence through the amp, but the volume controls of the iPhone are disabled.

Is there any way to make the iPhone output audio through its Dock connector, but still control volume in the normal way?

If instead, connecting to the amp from the headphone port, it is possible to control the volume, but that's another cable and a huge connector sticking out the top of the iPhone 4. So I want to find a way to still control the volume even when playing out the Dock connector.

 

[barbu]

I think the dock is likely outputting "line level" which is fixed and cannot be changed. You are expected to adjust the volume on whatever the dock is plugged into.

 

[UKenGB]

Well 'line level' doesn't have to mean it is fixed and if the device plugged in has no volume control (e.g. headphones), what then?

Specifically I am wanting to connect to a power amp (no volume control) and control the volume on the iPhone. It doesn't have to be an actual dock as there are cables with USB and audio jack one end and Dock connector the other. This might be used with e.g. headphones or a power amp, neither of which has volume control. In which case controlling volume on the iPhone itself is essential.

I know there is a pin in the Dock connector that is used to tell the iPhone when it's docked (and other conditions) so audio output can be switched to the Dock connector, but in some cases the audio is not switched when docked, only when the amp is plugged in. So the iPhone is sensing the amp connected to the analog audio output (not even sure how it does that) and as soon as the output switches, the iPhone's on-screen volume controls disappear and the buttons become inactive.

What I'm trying to figure out is whether it is possible for a Dock based iPhone (i.e. <= iPhone 4) to output audio via the Dock connector AND control the volume. It may be deeply embedded in iOS that audio out the Dock connector and NO volume controls are inextricably linked. But it may all just be a sensing thing that can be fudged. I know of one cable supplier who claims volume can still be controlled on the iPhone. We'll see when it arrives.

Then there's Lightning based iPhones (>= iPhone 5). Apple themselves produce a Lightning to audio jack for use with headphones that therefore MUST provide volume control on the iPhone and they say it's compatible with ALL Lightning iPhones with iOS 10 and above. But does that mean ALL Lightning cables with audio output (i.e. built-in DAC) therefore leave volume controls enabled on the iPhone even when sending audio out that way. Or is there some other sense mechanism that means it may keep volume control enabled, or it may disable it? In which case, what is that mechanism?

As I said, I want the iPhone to send audio out of its main connector (Dock or Lightning) to power amp while charging AND controlling the volume. I might want to use either iPhone type so would like to figure out the solution on both.

Anyone have any detailed knowledge/experience of this?

 

[barbu]

The apple universal dock has variable volume rather than line level. You can control the volume of the dock with the remote.

 

[UKenGB]

Not all their docks had the IR sensor for remote and in fact those seem to cause problems with no output at all, as indeed I'm experiencing with my IR docks. The other 'non IR' docks work, but iPhones volume control is disabled/hidden.

However, the IR docks control of the volume might have been done by signalling the iPhone to adjust the level, rather than it being adjusted in the dock's own circuitry.

Ideally I want to be able to just use a single cable, powering/charging to the iPhone, outputting stereo analog audio with volume controlled by the normal iPhone volume controls.

I'd really like details on how it all works so I can figure out what is and what is not possible.

 

[barbu]

I completely understand what you are trying to do. Most iPod docks only put out line level. The universal dock (like the one I use) has variable output by way of the remote control. This dock has a dac built in to it, so the iPhone isn’t producing the audio at all.
I can’t think of a way to do what you want other than using the headphone port instead.

 

[UKenGB]

Well for a Lightning iPhone, the headphone port IS the main port, so it MUST be possible to get volume controlled audio and charging through that one cable.

As for an iPhone <=4 dock having a DAC rather than using the line out already available, I'm not sure why you'd do that. Well, I can imagine some argument that their DAC is better than the one built-in to the iPhone, but I can't believe there's be any discernible difference in any audio likely to be sent from an iPhone.

But ignoring that, the question is, can an iPhone 4 send volume controlled analog audio out the Dock connector port? It obviously could technically, but Apple may have made it impossible. Or they may simply rely on sensing what's on the end of the cable and may in some cases leave the volume controls enabled on the iPhone. This is really what I'm trying to establish. What are the choices iOS has regarding audio output. Is it actually possible for iOS to output volume controlled audio through the Dock connector and if so, how and under what circumstances? Or have Apple hard coded it so audio out the Dock connector can only ever be fixed level? The latter seems rather Draconian (even for Apple's known desire to control everything we can and can't do), but if the former, how is it achieved? Physical sensing of the Dock connector pins, or some software signal?

I'm thinking an experienced programmer of iOS from that time would be able to answer this.

 

[barbu]

I won’t repeat myself any further. Line level is not a conspiracy, nor is it variable.
Only the universal dock has an integrated dac, it has nothing to do with what iPhone you have.
Anyway, good luck.

 

[UKenGB]

I'm not asking you to repeat yourself, but you have not actually answered the question and are in fact incorrect on several points:-

Line Level does not have to be fixed. I have and have had AV devices in which the line level output was variable with a volume control. When using a headphone jack output into an amp's line level input, that is also variable. Another example, using a pre-amp connected via line level to a power amp. One of the primary functions of the pre-amp is to vary the level. It's called 'volume control'.

It actually does rather depend on what iPhone. The iPhones 5 and later have a Lightning port and not a Dock connector and as I'm sure I don't actually need to tell you, they are completely different. Not only that, but the latest iPhones have no audio jack analog output, so all (wired) audio has to be through the Lightning port. This lack of headphone port may not actually make a difference to this question, but this variation cannot be dismissed since it directly relates to my question.

Are you sure Apple's Universal Dock has a built-in DAC? Why would they do that when the Dock connector includes analog audio. You may be right, but seems non-sensical to me. However, it is irrelevant to my question which is not about, nor anything to do with docks.

So far, I have found that every audio connection I have tried from an iPhone 4 (through its Dock connector/port, whether an actual dock or not is immaterial) to an amp results in the iPhone's volume controls being disabled.

However I have found a (Dock -> USB power and analog audio) cable whose supplier has stated that when using it the iPhone can still control the volume, as I desire. Whether this is actually true remains to be seen when it is delivered.

What I can confirm is that the equivalent Lightning -> USB + audio cable can charge the iPhone, play music to an amp and allow the iPhone to control the volume (ooh, variable line level, who'd have thought). That is fact as I just bought one and tested it and that is indeed how it works. So I will switch from trying to use the iPhone 4 to using a Lightning based iPhone as that can be used in the manner I require.

What is still unknown is whether the equivalent Dock cable can do the same. That has not been answered. Although no longer of vital important to me, it would still be good to know. But failing any actual answers here, it will have to rely on testing that cable I mentioned above. If it does allow volume control by iPhone, that will be good to know and means a Dock connector based iPhone can be used with a power amp (i.e. and control the volume). If not, I'll just forget the iPhone 4 and stick to the iPhone 5.