Hi,
Am 17.10.2014 um 14:51 schrieb Michael Mrozek mrozek@openpandora.org:
Am Thu, 16 Oct 2014 10:09:25 +0200 hat Dr. H. Nikolaus Schaller hns@goldelico.com geschrieben:
Hi,
First things first: The Amplifier of the PandaBoard is not that good. The more I increase the volume with ALSA, the worse the audio quality gets (it easily distorts).
Please can you describe your setup exactly? What I am missing is some definition which outputs you did use.
Pandora: Line-Out or headset jack?
Pandora: Line-Out
ok, this is DAC only and excludes the amplifier.
PandaBoard: Headphone or Handsfree Speaker?
PandaBoard: Headphone (the internal port)
ok, this already has a Class-AB amplifier included - and might be the reason why you see more noise.
I think the 5432EVM has a bypass mode to the third 3.5mm jack where the signals are fed out before the handsfree amplifier.
I had issues using the one you soldered on top - the peak always was way higher than standard line-out, so even with lowest volume setting, I couldn't record it without distortions.
That is what I meant with my warnings about measuring a class D amplifer output without proper low-pass filter or load.
This output is capable of driving 600mW - 1W into the new speakers. To make them really loud.
Maybe you can connect the speaker board I have added and the speaker. And then tap the signals arriving at the speaker.
For the records: the TWL6040 is designed for smartphone applications. Therefore it has 3 outputs:
1 earpiece (tiny power) 2 headset (low power) 2 handsfree/music speakers (high power)
Unfortunately not all of them are available on the PandaBoard/5432EVMs for evaluation.
Might've been an issue with the software setup as well though, I can retest that.
from the TWL4030 data sheet:
The stereo headphone path has a low-power (LP) mode operating from a 32-kHz sleep clock to enable over 100 hours of MP3 playback time. Very-high dynamic range of 104 dBA is achieved when using the system clock input and DAC path high-performance (HP) mode. Class-AB headphone drivers provide a 1Vrms output and are ground centered for capless connection to headphone, thus enabling system size and cost reduction. The earpiece driver is a differential class-AB driver with 2Vrms capability to a typical 32-Ω load or 1.4Vrms to a typical 16-Ω load.
This means the LP mode is indeed optimised for MP3 playback, i.e. not better than MP3 :) Technically it uses the 32kHz signal to derive its internal clocks (17/19MHz) and enables only the headset path (everything else on the chip is disabled and the CPU is not required to provide the 19 MHz clock).
So there should be no audible difference. But I remember that Peter mentioned some issue in the driver.
Finally this text confirms that the headset out has an *analog* amplifier (Class AB) with ~100 mW output power.
Once again we gained a little more understanding of the TWL6040 details...
Well, that low-power mode sounded like MP3 with 128kbps, which is horrible for me ;)
Indeed.
BR, Nikolaus