A speech signal, band limited to $4 \; \mathrm{kHz}$ and peak voltage varying between $+5 \mathrm{V}$ and $-5 \mathrm{V}$, is sampled at the Nyquist rate. Each sample is quantized and represented by $8$ bits.
The number of quantization levels required to reduce the quantization noise by a factor of $4$ would be
- $1024$
- $512$
- $256$
- $64$