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joegorin

Bit-Perfect Streaming Should be Possible with Bluetooth; Is It?

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Like the dozens of enthusiastic people asking for DLNA support, I want to stream from a portable device (a tablet I purchased solely to be a Poweramp dedicated mp3 player) to my stereo. It is possible that Bluetooth, not DLNA, is the answer.

 

As interested readers know, DLNA is a wireless standard capable of the transmission of audio from portable devices to WiFi receivers at CD levels of fidelity. Poweramp does not support DLNA, but some people have succeeded in connecting it to Audio Cast via BubbleUPnP in a rooted phone. (I have succeeded in doing that with an HP Touchpad running Cyanogenmod and Android KitKat, but this setup does not work acceptably for me because, even without wireless transmission, Poweramp stops playing every few hours, which does not meet my needs. And, yes, I have turned off all the likely features causing this such as gapless processing and fading.)

 

I want to make a system that works on a Dell tablet with Android/KitKat. To use Poweramp in this case requires rooting the tablet. This I have been unable to do, and do not want to do because it is not sustainable through OS updates. Also, my WiFi seems to occasionally cause another trial system I am using (n7player using Toaster Cast) to stop playing every few hours or less, despite careful reconfiguration of the channel used by the WiFi router to avoid interference with the DLNA machine that is configured as another network. So I am anxious to try the Bluetooth alternative.

 

Bluetooth has an available bit rate well in excess of the bit rate of any mp3 files--it is about  1 MB/s, while mp3s usually go no higher than 320 kb/s. So if the transmitter (Poweramp and the Dell tablet) is willing to send the mp3 files, and the receiver is willing to receive them, Bluetooth should be good.

 

What we need is 1) a Bluetooth standard that supports this concept, 2) a Bluetooth receiver that supports it, and 3) Poweramp, combined with my tablet, that supports it. Bluetooth does support it. I am pretty sure that most $20 Bluetooth receivers do not, but I have found at least two that do: Nyrius Songo HiFi Wireless Bluetooth aptX Music Receiver ($50) and Audioengine B1 ($190). There is an article that addresses the issue but suggests that Poweramp and my tablet will not do their part in this coordination:

 

You may be familiar with prolific and well-respected audio journalist Brett Butterworth. He wrote, "If both the source device (your phone, tablet or computer) and the destination device (the wireless receiver or speaker) support a certain codec, then material encoded using that codec does not have to have the extra layer of data compression added. Thus, if you're listening to, say, a 128 kbps MP3 file or audio stream, and your destination device accepts MP3, Bluetooth does not have to add an extra layer of compression, and ideally results in zero loss of quality. However, manufacturers tell me that in almost every case, incoming audio is transcoded into SBC, or into aptX or AAC if the source device and the destination device are aptX or AAC compatible." You can find the whole article here:
 
 
 
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Comparing AirPlay, Bluetooth, DLNA, Play-Fi, Sonos and M...
A comparison of AirPlay, Bluetooth, DLNA, Play-Fi and Sonos wireless audio technologies
 
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The reasons why include adding beeps for your phone, and using the volume control on the phone or tablet...to say nothing of the equalizer available in Poweramp.

 

In Poweramp promotional material here:

 

http://powerampapp.com/features/

 

...is the inference that the audio can stay in mp3 form even as Poweramp runs its equalizer. Under the "Equalizer and Tone" heading is this: "works for any supported format and for bluetooth A2DP headset" (A2DP is the transmission standards that deal with negotiating format between the transmitter and the receiver).

 

So, my questions are:

 

1. Is the transmission of Bluetooth signals a function of the operating system or the app or both?

2. Can, or does, Poweramp act to allow direct transmission of mp3 files from the player via Bluetooth to a compatible receiver?

 

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Answering part of my own question, let me quote what CWD, who supports the Nyrius Songo, wrote to me after a few email exchanges. "I have confirmed that whenever any audio is played through Bluetooth, it is recompressed and encoded either using SBC or APTX, this will result in a loss in quality more so on the standard Bluetooth devices, less so on APTX capable transmitters. Because the Songo HiFi connects using an Aux cable, what codecs the destination device support is a moot point it is not like a USB connection that may be able to differentiate. Unfortunately if you are looking for 100% reproduction, this may not be the product for you..."

 

So we know that one maker of an aptX-capable Bluetooth receiver thinks it will not allow lossless transmission of mp3 files in general. So I think Butterworth is right that avoiding transcoding is not currently possible in practice, even though it is in theory.

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