Generate frequency using sox, bad quality

I am now using the SOX library to generate a sound file with different frequency and waveform.Sometimes, I need to combine more than 20 frequencies together in a single sound file. I will use the command like the following

./sox -e a-law -r 44100 -n output.wav synth 5 sine 3 square 250 sine 300 ...

However, sometimes the output file have many noise. If I remove -e a-law argument the output will have no sound.

./sox -r 44100 -n output.wav synth 5 sine 3 square 250 sine 300 ...

I am new to use the SOX library. Does anyone know how to generate the frequency with high quality output? Or any other alternatives to generate the frequency.