Bluetooth audio output gain

[TwoEyedJack]

Hello, I have this issue with a number of Bluetooth sources and receivers regarding low output signal level. More specifically the maximum audio signal I can get when playing music from a Bluetooth source like a smartphone or a computer is usually not enough to drive the amplifier to good levels of output power. Some of my Bluetooth receivers even on their max volume they play too quiet, while others don't. Ι suppose this has something to do with either the output voltage being to low or the input sensitivity being to high or the gain of the amp being to low (i am not sure if input sensitivity and amp gain is something different). One of my amps has propably to high of a gain (input sensitivity 600-800)and it works fine with all my Bluetooth players while the rest require me to use a digital "preamp" like the one found in VLC player or a similar app for smartphones. Why even though i can up the "gain" through software without it clipping the Bluetooth players output such a low digital signal? Is there a better way to remedy this issue besides getting a better Bluetooth receiver or connecting a pre-amp? (I am not talking about hi-fi audio here just consumer amps/players in low fidelity systems like boomboxes or desktop speakers)

 

[wwenze]

Generally speaking, phones and low-powered devices like Bluetooth receivers will have a max output of around <1Vrms.

In order to generate the "standard" 2Vrms will require the source to be able to swing 5.656V of voltage. Add some margin needed for power supply, and you'll need something powered by at least 6V to 9V PSU. So if you scale down your PSU voltage - Lots of cheap electronics run on 5V nowadays - expect a corresponding drop in max output voltage to <1Vrms.

"Gain" through software works something like this: .WAV file says output a DAC value of 50. "Software gain" takes this number, multiply by, say, 2. So now it outputs a value of 100. This works fine until the file contains a value of 200 and software gain makes it 400, but your DAC only has a max value of 255 resulting in clipping.

One thing to note is oftentimes Bluetooth receivers have their own volume control, and your phone has its volume control too. Normally this isn't a problem with high-output-voltage devices like computers and TVs, but when you have a low-output-voltage device in your chain i.e. the BT receiver, this usually requires setting at least the BT receive or the phone OS volume to max volume.

tl;dr when using phone for BT, make sure phone volume is set to very high. If that still fails, get a BT receiver powered by mains.

 

[Chrispy]

Why the hell use bluetooth in the first place?

 

[levimax]

Why the hell use bluetooth in the first place?

cheap, easy, allows anyone with a smart phone to play their music on any bluetooth system, sound quality, especially for the higher end codec, is very good.

 

[Chrispy]

cheap, easy, allows anyone with a smart phone to play their music on any bluetooth system, sound quality, especially for the higher end codec, is very good.

Still better to just use wifi. BT is second place at best. (only way I use my smartphone/tablet for streaming)

ps but depending on devices, may or may not resolve your issue with levels.

 

[TwoEyedJack]

Generally speaking, phones and low-powered devices like Bluetooth receivers will have a max output of around <1Vrms.

In order to generate the "standard" 2Vrms will require the source to be able to swing 5.656V of voltage. Add some margin needed for power supply, and you'll need something powered by at least 6V to 9V PSU. So if you scale down your PSU voltage - Lots of cheap electronics run on 5V nowadays - expect a corresponding drop in max output voltage to <1Vrms.

"Gain" through software works something like this: .WAV file says output a DAC value of 50. "Software gain" takes this number, multiply by, say, 2. So now it outputs a value of 100. This works fine until the file contains a value of 200 and software gain makes it 400, but your DAC only has a max value of 255 resulting in clipping.

One thing to note is oftentimes Bluetooth receivers have their own volume control, and your phone has its volume control too. Normally this isn't a problem with high-output-voltage devices like computers and TVs, but when you have a low-output-voltage device in your chain i.e. the BT receiver, this usually requires setting at least the BT receive or the phone OS volume to max volume.

tl;dr when using phone for BT, make sure phone volume is set to very high. If that still fails, get a BT receiver powered by mains.

I see, indeed one of the devices i was referring to works with a simple 5v adapter but the other two ( being amplifier boards with integrated Bluetooth chips work on 24v and 21v respectively) one of them has no issues during playback while the other is the one that gives me trouble, maybe the first one has high amplification gain and it counter-acts the low bt output..?
Regarding software gain, so this workaround would only work on music that has been mastered in a relatively low level while better mixed tracks would reach maximum loudness without the need of software "gain". Is there any other problem with using the software gain like this as long as I don't overdrive the dac? (volume on smartphone is always on max ofcourse but i have noticed that when setting the smartphone volume lower than max i can take the software gain higher without clipping, I suppose this is because it uses digital attenuation of the signal)

Still better to just use wifi. BT is second place at best. (only way I use my smartphone/tablet for streaming)

ps but depending on devices, may or may not resolve your issue with levels.

Sure but it goes without saying that this is not practical in a boombox/portable Bluetooth speaker application.. hence the name...