Home › Forums › Sparkfun MP3 Shield Library Support Forum › Adding an LED.. › Reply To: Adding an LED..
Extrace from http://www.vlsi.fi/fileadmin/software/VS10XX/vs1053b-patches.pdf
Where the below documentation is from the current patch from their website and is more recent patch. That I have not converted to the SFEMP3 file binary format. So the library has the old version. There is a vs_plg_to_bin.pl in the repo for creating new binary files from their patches.
VU Meter
SCI_STATUS bit 9 enables VU meter, which calculates a leaking peak sample value from both channels and returns the values in 1 dB resolution through SCI_AICTRL3. The high 8 bits represent the left channel, the low 8 bits the right channel.
Note that the following has changed from the previous release.
Values from 0 to 96 are valid for both channels. 0 means no sound, 96 is highest level. In practise the highest value will be 95, the signal is probably clipping if you get 96.
The calculation does not take the volume setting into account.
The VU meter takes about 0.6MHz of processing power with 48 kHz samplerate.
_______
from wikipedia i read:
<span style=”color: #252525; font-family: sans-serif; font-size: 14px; line-height: 22.4px;”>0 VU is equal to +4 [dBu], or 1.228 </span>volts<span style=”color: #252525; font-family: sans-serif; font-size: 14px; line-height: 22.4px;”> </span>RMS<span style=”color: #252525; font-family: sans-serif; font-size: 14px; line-height: 22.4px;”> across a 600</span>ohm<span style=”color: #252525; font-family: sans-serif; font-size: 14px; line-height: 22.4px;”> </span>load<span style=”color: #252525; font-family: sans-serif; font-size: 14px; line-height: 22.4px;”>, or about 2.5 milliWatts</span>
