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Old 03-12-2008, 07:37 PM
woof woof is offline
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Default Questions of Bluetooth profile, over-modulation, etc.

Hi everyone,
I'm I NuBee to this forum but a long-time self-described "audiophile" (of sorts). I've been playing around with the 8gb Pilot and have some in-depth, mostly Bluetooth related questions. I apoligize in advance for such a wordy 1st posting.

I've found the Pilot's headphone output, when used as a line-output (with a 10-15kohm load), to be fairly clean and balanced (at least for a DAP). Using a variety of wired headsets it sounds OK, just not particulary strong, and like all DAPs it's power output stage seems sensitive to the whims of the electrical signature of the headset (resistance, inductance and to a lesser degree capacitance). But hey, all DAP's work off a single-ended, very low-voltage power supply and an amplifier with a slew-rate and damping factor of...well...not much, but I digress.

Using BT stereophones however has been a far less than satisfactory experience. I knew using BT for audio would result in a significant loss of dynamic range and frequency response but I was quite unaware of the amount of good ol' distortion and artifacts it would produce (having a situation where portable cordless is needed).

In trying to locate the source(s) of the distortions, I found that the Pilot equalizer has some effect on a distortion that sounds much like over-saturation (clipping). I believe Digialdel mentioned that the input to the BT encoder was fed a maximum volume signal all the time to provide the best S/N ratio for the BT link. It seems to make sense that reducing the BT input signal by using eq would help some. There also seems to be other BT distortions that I cannot pin down or correct. These sound like "grittyness" or "raspyness" on the edge of vocals, horrid smearing/distorting of cymbols, etc. I've tried all flavors and types of file encoding rates from MM and none seem alter this phenominom.

It was mentioned somewhere that the Pilots have BT version 1.2. Looking the Pilot up at the following site: https://www.bluetooth.org/tpg/QLI_viewQDL.cfm?qid=13059 indicates the Pilot's BT license was for 2.0/2.0+EDR (extended dynamic range) Edit Corrected to: Expanded Data Range. My limited knowledge of BT has led me to believe that it is possible for 2.0+EDR to enhance audio transmission but that it is an spec option, and not manditory for 2.0 devices. And both transmitter and receiver must have the profile for the link to function at the higher bitrate. Also from what I understand there seems to be no difference in the audio quality (bitrate) between 1.2 and 2.0 but there is between 1.2/2.0 verses 2.0+EDR. So my first question is: Is the Pilot BT 1.2, 2.0 or a fully-enabled 2.0+EDR? Edit: I figured out the answer...it's BT Core 2.0

This leads to my second question. Since these DMP manufacturers jealously guard information, like simple block diagrams of signal flow, I was wondering if it would be possible in a firmware revision to relocate the Pilot's master volume control so it is in-line before the BT encoder; sortof the way it is with the Samsung P2? That way the user could set the level for best encoder matching verses maxium BT volume (unfortunately the P2's eq doesn't work over BT). Alternatively, I think this volume control relocation would not be needed if ReplayGain or some other method of controlling codec playback volume was added.

As to the other sources of distortion, could it be simply the sampling rate of the BT encoder, especially if it's BT 1.2 or 2.0 or an encoding error with what may be an internal PCM or equivant bitstream? I've ruled out obvious external possiblities like interfearence, signal strength, etc.

BTW, the only BT headsets I've tested to date are the Sony DR-BT22, Sony DR-BT50 and the Insignia.

Also has anyone listened to a true, fully enabled profile 2.0+EDR audio source (i.e. a DAP with a SonyWLA-NWB1 or TMR-BT81P transmitter, a 2.0+EDR USB computer dongle, etc.) with matching profile headset?

Thanks to all in advance. Great forum here.

Woof
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