Upsampling PCM audio: from 6 kHz to 8kHz What would a straight-forward way to convert an audio payload (PCM 16bit) from 6 kHz to 8kHz? I understand that this is an interpolation problem. 

I fear that a linear interpolation would introduce too much noise. If so, what would be a better interpolation? I was looking at Lanczos resampling but I've seen it used in image scaling only and not sure it's worth it for audio.

I'm using Java.  I've found the JSSRC library butI would have prefer something more lightweight. Beside, I'm not sure this is really necessary for low-frequency audio (which happens to be decoded from ADPCM).

BTW, I'm not interested in creating a WAV having a 6 kHz frequency header, I really want to resample.
If processing cost is not a problem, you may use the following algorithm for sample rate converting your data from 6 khz to 8 khz.

1- expand your signal x[n] by 8, producing xe[n] (insert 7 zeros after every sample of x[n])
2- design a low pass filter hlpf[n] with a gain of 8 and cutoff frequency pi/8
3- process the expanded signal with this lowpass filter = xef[n]
4- compress output of the filter by 6 via selecting every 6th sample: y[n]=xef[6n]
(NOTE: You can also do this with 4:3 upsample and down sample, with a new filter,  which would require less processing cost)

Lowpass filter must be sharp enough to ensure proper anti-aliazing. If this is too much overburden for  simple rate conversion then try high order polynomial resampling. That could also be costly however.