What are these transistors doing and how are they working in this VU Meter?
I built a project with LM3915s almost 40 years ago. The part has a programmable current sink so you can connect LEDs directly to it. Depending on the color, you can put 4 or so LEDs in series at 12V. Four red LEDs for sure, since that is what I used. More than this, you can use a PNP, but you should still put some in series so you don't waste a lot of power in the resistor. For your design you seem to want 6 LEDs in each circuit, I would put 3 in series, each path needs a resistor. The transistor will saturate, so you need to limit the current.

Rough calculation for the series resistor: Vce = ~0, each red LED drop = ~2V 

R = (12 - 2 * 3) / 10 mA = 600 ohms







simulate this circuit &ndash; Schematic created using CircuitLab

Edit: Another idea: The LM3915 is not expensive, use two, then you can use 12V without transistors. Send your audio input to both. Divide the 6 LEDs into two groups, 2 &amp; 4 or 3 &amp; 3. 

Note that the original manufacture doesn't make these anymore, you are most likely buying a Chinese clone. Therefore, they may not match the datasheet exactly.