t%(t&t>>1) 

 (t&t>>12)*(t>>5&12)*t>>12 

 0x7E8^(t&t>>12)*t>>12 

 t>>8+t&t 

(128+127*sin(t/10))*((t>>10&3)+1)*(1+cos(t/10))

128 + 127 * sin(t / 1000): Generates a sine wave oscillating between 1 and 255. The frequency is scaled so that it fits within the 8 kHz sample rate. t / 1000 adjusts the frequency of the sine wave.
(t >> 10 & 3) + 1: Extracts a 2-bit pattern from t and adds 1 to make sure the result is always non-zero. This introduces variation based on the bitwise manipulation of t.
1 + cos(t / 5000): Adds a cosine modulation factor. The cos(t / 5000) oscillates between -1 and 1, so adding 1 scales it to range from 0 to 2. This modulates the amplitude of the waveform.

BPM=120,SAMPRATE=40960,T=t/SAMPRATE*BPM/60*32768,tri=(x,y)=>abs((x%y)-y/2)*2,high=x=>t*2**([0,3.5,7,10.5,14,17.5,21,24.5,24.5,21,17.5,14,10.5,7,3.5,0][(T>>14)&x&15]/12)/4&63,h1=tri(high(15),64),bass=x=>(t/16*[1,1,1,1,1,1,1,1,1.35,1.35,1.35,1.35,1.5,1.5,1.5,1.5][(T>>14)&x&15]&47),b1=tri(bass(15),64),h2=tri(high(13),64),b2=tri(bass(13),64),h3=tri(high(11),64),b3=tri(bass(11),64),kick=sin(sqrt(T/128%256)*16)*32+32,snare=(t*sin(T>>3)*(T>>15&1)&63)*(-T>>13&7)/3.5,[h1,h1+b1,h1+b1+kick,h1+b1+kick+snare,h2+b2+snare,h2+b2+snare+kick,h3+b3+snare,(h3+b3)/3+(h2+b2)/3+(h1+b1)/3+kick+snare][(T>>19)%8]

((t & (t >> 7 | t >> 8 | t >> 20) + t) ^ t)

x=(t,y=256)=>(t/4*(4|7&t>>15)>>(~t>>13&1)&128|t/4*(t>>13&t>>15)*(~t>>11&3)&127)%y,l=16,(t?f+=x(t)-f/l:f=0),[f/l,(x(t)+x(t+1)+x(t+2)+x(t+3)+x(t+4)+x(t+5)+x(t+6)+x(t+7)+x(t+8)+x(t+9)+x(t+10)+x(t+11)+x(t+12)+x(t+13)+x(t+14)+x(t+15))/16]

max(0,min(128,((b=(-t*1.0595**(("0010010030705503"[t>>13&15])-12+3*(t>>18&1))&255),c=(b**3)>>5,(sin(b*(.2+sin(t/6e6))*.2))*c+c)*(-t&8191)>>18)))-((sqrt(t&8183)<<6&64)*(((t>>15)&1)^(t>>13))-(t&15))*(t>2<<19)+((t&16383)*(-t>>3&511)/7e4)*random()*(t>1<<19)