Some notes on audio routing

lbendlin · Posted: Sat May 12, 2012 4:03 am Post subject: Some notes on audio routing

With version 601 we have introduced a new option for the audio routing - Bluetooth mono headsets. Since audio routing in Android is a royal mess I thought it would be helpful to discuss the new options in some more detail

Default: The sound will come either out of the device speaker, or if a stereo bluetooth speaker is connected (also known as A2DP or advanced audio distribution profile), it will come through that bluetooth speaker. If you have headphones plugged into your device the sound will go through them

Device speaker: No matter if you have a Bluetooth Stereo speaker or a Bluetooth headset connected, or even headphones plugged in, the sound will come out of the device speaker.

Bluetooth headset: IF (and only if) you have a bluetooth mono headset (also known as SCO) paired and connected the sound will go through that headset. If no bluetooth headset is connected, the sound will go through the device EARPIECE (not speaker) or if you have headphones plugged in, the sound will go through these.

Having said all that, both "Device Speaker" and "Bluetooth Headset" options are hacks that basically trick the device into thinking that it is on a phone call. This may yield poor audio quality on some BT headsets, and may simply not work on others. Feel free to blame Google for that (and for the lovely bug in ICS that asks for unneeded permissions when you want to enable SCO). If it is any consolation - Apple do not even permit routing sound to the BT headset, supposedly due to the poor sound quality.

So - if it works for you - pat yourself on the back. If it doesn't - use another option and carry on with your life.
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MaFt · Posted: Sat May 12, 2012 8:28 pm Post subject:

For clarity can you confirm (or deny) that a Bluetooth Headset is different from Bluetooth Handsfree?

eg my car has an old Nokia CK-7W which I class as a handsfree and not just a headset as it does all sorts of stuff like activating the voice calling etc. Or am I just confused?

MaFt

Edit to add: The manual says that the CK-7W "is intended for use with any mobile phone that supports the Bluetooth Handsfree Profile (Bluetooth HFP)."

lbendlin · Posted: Sat May 12, 2012 8:36 pm Post subject:

Android does not support the handsfree profile, at least not through the SDK. Only Headset (SCO) is supported.
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Kremmen · Posted: Sun May 13, 2012 6:09 am Post subject:

So if your phone is paired to your car bluetooth connection and you get or make a call will it still allow the call to go ahead via the car to phone link ?
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lbendlin · Posted: Sun May 13, 2012 2:30 pm Post subject:

Technically yes. However, the current version (601) does not check for an ongoing phone call and will mess with the call audio when "Bluetooth headset" is selected. This will be fixed in an upcoming version (if a call is ongoing, no alert will sound).
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bigwol · Posted: Thu May 17, 2012 1:33 am Post subject: Bluetooth Camera Alert

The new Bluetooth Headset option almost does what I want, but not quite!

My Android phone is paired with my JVC bluetooth car stereo.

Previously if I wanted Camera Alert warnings an alerts I had to be on an active bluetooth source from the phone - eg Amazon MP3 or similar, and it would interrupt the music with the Warning.

This was ideal, but only on the bluetooth audio source.

I usually listen to FM radio on the way to work, and in this mode the Camera Alert warnings don't come through the stereo.

With the Bluetooth headset option in the latest release, any alert interrupts the FM Radio and works fine - until you want it to release the audio back to the selected source - it never goes back, and displays 'waiting for voice' and just sits there in silence -

The only way to kill the Camera alert latched possession of the audio stream is to power off the radio and back on again - completely unusable.

Furthermore, the default doesn't work as well as the old one in bluetooth audio mode, theough I haven't tested it properly yet.

Can't we have an 'Interrupt whatever source is selected' but give it back after the warning - mode?

lbendlin · Posted: Thu May 17, 2012 2:47 am Post subject:

this might be a limitation of your car stereo (is it expecting a voice command maybe?). We're closing the BT connection as soon as we are done.
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MaFt · Posted: Thu May 17, 2012 8:58 am Post subject:

bigwol · Posted: Thu May 17, 2012 5:15 pm Post subject:

I think it may be triggering the Voice Recognition Dialling inadvertantly, and because I don't use this, and there are no voice tags stored, there's no way out.

Here is the spec on the Radio

JVC KD-R921
1-DIN CD Receiver

Bluetooth® Wireless Technology Dual USB/CD Receiver with Front AUX.
Specification

MOS-FET 4 x 50W
TI/Burr-Brown 24-bit DAC
5-Band Parametric iEQ
Bluetooth® Wireless Technology*1 (USB Bluetooth® adapter included)
USB Audio for iPod®/iPhone® etc.
2-Way Control for iPod®/iPhone®*2 (Head Unit/iPod® or iPhone®

(Phone Book Access Profile, Phone Book Transfer, Hands-Free Call, Audio Streaming, SMS Receipt Notification, Voice Recognition Dialling, Compatibility Check Mode, Connects 2 Phones)
Front/Rear Dual USB Ports (WAV/MP3/WMA/iPod® & iPhone® Audio)
2 Connections for iPod®/iPhone®
Application Mode for iPod®/iPhone®
MP3/WMA/WAV*3 Compatible with ID3/WMA Tag (CD/USB)
Radio Data System Tuner
HS-IVi Tuner
Time Alignment (DSP)
DSP: Time Alignment
Loudness Control in 3 Patterns (DSP)
Loudness Control in 3 Patterns
Digital Track Expander (DSP)
High-Pass Filter/Low-Pass Filter (DSP)
5.0V Line and Subwoofer Pre-Out Level
3 Gold-Plated RCA Pre-Out Terminals (Front + Rear + Subwoofer)
Subwoofer Control
Front AUX-IN
Separated Variable-Colour
Detachable Face Panel
Steering Remote Control Ready
*1 Available functions depend on mobile phone.
*2 Compatibility with 2-way control for iPod®/iPhone® differs by model.
*3 Not available on CD

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