A-law and u-law are two algorithms that are used in modifying an input signal for digitization. These algorithms are implemented in telephony systems all over the world. The two algorithms have a fairly minimal difference and most people would not know the difference. The first difference between the two is the dynamic range of the ouput; U-law has a larger dynamic range than a-law. Dynamic range is basically the ratio between the quietest and loudest sound that can be represented in the signal. The downside of having a higher dynamic range is greater distortion of small signals. This simply means that a-law would sound better than u-law when the sound input is very soft.
The advantages and disadvantages of one over the other are fairly insignificant and both are currently in use in different areas of the world. U-law is currently being used by companies in North America and in Japan while A-law is being used in Europe. Other areas use a mixture of the two depending on the country.
Most countries use only one standard so there should be no problems with local call or even with international calls between countries that use the same standard. A problem arises when a call is made from a country that uses one standard to a country that uses the other standard. Although it is possible to facilitate a conversion from one algorithm to the other, this would be a lossy conversion and the result would be a degraded signal. To avoid the problem, a-law is the algorithm that would be used whenever either side uses a-law. Because of this, it is necessary for countries that use u-law to also have the capability of using a-law while countries that use a-law do not necessarily have to be able to do u-law.
Summary:
- U-Law has a larger dynamic range compared to A-law
- U-Law has worse distortion with small signals compared to A-law
- U-Law is used in North-America and Japan while A-law is commonly used in Europe
- A-law takes precedence over u-law with international calls