// we assume that each entry in data[] is an int in [0,127]
    public byte[] getByteArrayRepresentation() {
        byte[] result = new byte[data.length/2];
        for (int i = 0; i < result.length; i++) {
            tmp = ((int) (data[(i << 1)] * 2)) << 4;
            tmp = (tmp | ((int) (data[(i << 1) + 1] * 2)));
            result[i] = (byte) (tmp-128);
        }
        return result;
    }

    public void setByteArrayRepresentation(byte[] in) {
        for (int i = 0; i < in.length; i++) {
            tmp = in[i]+128;
            data[(i << 1) +1] = ((double) (tmp & 0x000F))/2d;
            data[i << 1] = ((double) (tmp >> 4))/2d;
        }
    }