How to preserve or protect audio signal when lossless compression to get ODG=0?

Hi everyone

I do lossless compression on audio using the bitpersample variation method

My original audio has 2 channels, 24 bits per sample and .wav codec format

I compressed it into audio with 2 channels, 24, 16 and 8 bits per sample with the for codec .flac

When measuring objective difference grade (ODG) on .flac audio with 16 and 24-bit samples compared to the original file there is no problem (ODG=0)

However, when checking the audio .flac bitpersample 8 compared to the original file the result becomes -3 (Annoying)

Someone said audio compression process with bit per sample variation will decrease waveform or quantization error due to systematic process and not noise

How to solve the problem? so that the audio can be protected to get ODG=0?

I need your help guys

Thank you

[Sisi Misi]

can you help me guys ?