2 questions about TGrains

If anyone is using Tgrains Ugen.
Q1. It works fine for me on 1 channel buffers. but when I use 2 channels I get nothing. I am using the same code (see below) just change the numChannels input in the Ugen and load one of the stereo channels into the buffer before sending to TGrans (i.e. use Buffer.readChannel instead of Buffer.read).

({var src, pos=~ba.duration*rrand(0,0.9), env, dur=3;
	src = TGrains.ar(2,Impulse.ar(400),~ba,0.2,Line.ar(pos,pos+0.07,dur),LFNoise0.kr(30,0.01,0.2),0,1);
	env = EnvGen.ar(Env.perc(0.01,1),timeScale: dur, doneAction: 2);

Q2. When I use Impulse.ar(100) as the trigger I get vaguely pitched sound. Which is what I expect. Except that the pitch is 10% higher then it should be. It is comparable to SinOsc.ar(100). The same for 200 rate Impulse (which has 220Hz ). This could have been a 48000 vis 44100 samplerate but the soundfiles are 48000 and I also work at 48000 in SC. Any ideas?
many thanks

the documentation does state the buffer needs to be mono - TGrains | SuperCollider 3.12.2 Help

It must be a one channel (mono) buffer.