Bluetooth A2DP profile and poor sound quality

Question

I bought a YMB-10 module recently. This is a Bluetooth wireless audio receiver you can connect to your stereo to listen to music played from your mobile or laptop etc.

I tried to play some music from my laptop computer (with an Asus BT-183 Bluetooth module) and the sound quality was really poor. What's more, I could hear an extremely annoying, high pitched sound in the background, all the time.

Then I checked the receiver with a BlackBerry 8250 phone and the sound quality was much better. I checked it with a few different mobiles and the sound quality differed.

I would like to listen to good quality music from my laptop computer. I'm considering buying a new Bluetooth USB adapter, but I don't know whether or not it is going to help.

Could you please advise me what I should pay attention to when selecting one?

And why does the sound quality differ so much depending on the equipment I use to play music from?

Solution 1

Your music is likely going through several transformations:

1. Digital music file
2. Converted to analog sound wave (music player on laptop)
3. Converted back to digital signal (Bluetooth encoder)
4. Converted back to analog sound wave (Bluetooth decoder)
5. Turned into physical sound waves (Headset/speaker system)

The YMB is performing step #4. Each step introduces audio quality degradation.

For maximum audio quality, some Bluetooth A2DP receivers understand more codecs besides the single, required SBC codec. This can eliminate steps 2 and 3.

Also my guess is the Bluetooth SBC codec does not have the best audio quality. Ideally, the audio codec used should be lossless, but even lossy codecs like MP3 can sound acceptable. I am not sure if any Bluetooth products that support lossless audio have been released.

Finally, the other stages of the list above must all understand the Bluetooth protocol properly (music player, bluetooth encoder).

So, to answer your question: find a Bluetooth receiver that understands a better codec than SBC (ideally lossless). Make sure the rest of your Bluetooth "stack" also understands the same, better codecs.

More info: Advanced Audio Distribution Profile#Support of Codecs

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Update: As I said, a lossless Bluetooth audio solution may not be availalbe (I've found a lot of announcements, but no actual products) but it may also be overkill unless you're a serious audiophile. Simply using a non-SBC codec may be enough, but few products are marketed with those technical details.

You may get a lot of returns simply by ensuring that your YMB and A2DP source are using a non-SBC codec. (The (software) Bluetooth encoder on your laptop may simply not support the proper codec. I'd check into this, since you said your other sources sounded acceptable. Your results may vary with the type of audio file you are playing!)

Also, I considered alternatives to Bluetooth A2DP like wireless audio via 802.11. One such solution is the Apple Airport Express with Airtunes. (Plus software for non-iTunes/Apple applications.)

Solution 2

I've been making a BT receiver boombox for a friend to use in his work van and came accross the "Bluetrek ST1", amazing reviews regarding sound quality and I've simply broken it down (it was bought spares/repair) and rewired it directly to the input of the amplifier's RCA from the headphone outputs. It supports A2DP and AVRCP and has its own noise filters and frequency boosters.

I finished all the wiring yesterday and gave it a quick "blast", it does indeed sound very nice with clear deep lows and crisp highs, doesn't seem to have a problem with any "background" noise at all.

If you can find a cheap Bluetrek ST1 (the arms were prone to snapping on the earlier models), I would suggest removing the ear-bud sounders and wiring on a 3.5mm jack or an RCA cable.

The mods I made were significantly more complicated as I moved all the buttons to a front panel, made it a power regulation circuit and a VOX switch to turn everything off when not in use. But headphones to RCA is the basic output I'm using, and it sounds great.

Let me know if you need a advice modifying your ST1, I've copied down all the wiring and compressed everything to fit the size of a matchbox.

Comments

[Mariusz Schimke]

Thanks for a detailed answer! I'm still trying to find a proper adapter but without success. Yet :). I'll let you know if I find anything.

[Mariusz Schimke]

The only adapter I managed to find so far is Jabra A320S, promising "exceptional stereo audio quality": nextag.com/GN-Jabra-A320S-Stereo-557377649/write-reviews-htm‌​l. What do you think about it?

[Mariusz Schimke]

BTW, I've found some info about the SOUNDabout lossless codec for Bluetooth (by OINA), but can't find any adapter supporting it. Pity :(.

[Leftium]

@Mariusz: added some updates + the Jabra BT3030 was recommended to me in this other question: superuser.com/questions/36310/…

[whitequark]

I'm absolutely sure that if you use bluetooth USB dongle (as opposed to A2DP analog transmitter with headphone input jack), steps 2 and 3 will not happen as you wrote them. The driver in the OS will receive digital PCM stream directly from player and will push it to the dongle. The variant "2. Encoded with BT codec [SBC or whatever]; 3. Decoded back" would be more correct.

[Mariusz Schimke]

@Leftium: I've found another BT transmitter: uk.store.creative.com/Products/…. It supports the lossless APT-X codec and the one you mentioned (SBC). But please, tell me something. Is the codec a software- or hardware-related matter? I'm just unsure if the receiver (in this case my Yamaha YMB-10) will support the new codec. Sorry for bothering you and thanks for your help!

[Leftium]

@Mariusz: The codec can be implemented in either hardware or software. The key is both the Bluetooth source and receiver need to support the same codec. Otherwise they will negotiate the only common codec: SBC.