== Recording a sound==
A sound is recorded by making a measurement of the amplitude of the sound at regular intervals which are defined by the "sample rate". The act of taking the measurement is often called "sampling" and each measurement unit is called a "sample". A file which contains samples is often called a "sound sample" or "audio sample".
Other representations such as "ADPCM" ("Amplitude Delta Pulse Code Modulation"), encode or compress the data to reduce the size of the audio file. Samp2cdt can't understand these representations, so please use "PCM" only.
[[Image of the amplitude/time graph showing the waveform of the original sound:wave1.gif]]
[Fig 1. An amplitude/time graph showing the waveform of the original sound]
[[Image of the amplitude/time graph showing the waveform of the original sound:wave2. The measured amplitude and sample times are indicatedgif]]
[Fig 2. An amplitude/time graph showing the waveform of the original sound. The crosses indicate the amplitude measured at each sample time and the dotted lines indicate the the time of each measurement. The duration of time between each dotted line, defined by the sample rate, is equal to the duration of a sample. From this it can be seen that each sample has a finite and equal duration.
[[Image of the amplitude/time graph for the original waveform:wave3. The waveform generated by sampling is indicated by a dotted linegif]]
[Fig 3. An amplitude/time graph showing the waveform of the original sound. As in Fig 2, the crosses indicate the amplitude measured at each sample time. The dotted line shows the waveform generated by sampling. The final value of each sample is defined to be the amplitude measured at the time of measurement.
[[Image of the amplitude/time graph for the sampled waveform:wave4.gif]]
[Fig 4. An amplitude/time graph showing the sampled waveform. This waveform was generated at a high sample rate, and therefore the resulting waveform has a shape which is similar to the original. This waveform is the type you can see in a audio recording program like Goldwave.
[This image shows the same information as Fig 2, but using a low sample rate[Image:wave5.gif]]
[Fig 5. An amplitude/time graph showing the waveform of the original sound. As in Fig 2, this graph shows the amplitude of each measurement, and the dotted line indicates the time of measurement. This graph was created using a low sample rate. Notice that the time between each measurement is longer compared to Fig 2.
[[Image:wave6.gif]]
[This image shows the same information as Fig 3, but using a low sample rate
[Fig 6. An amplitude/time graph showing the waveform of the original sound. As in Fig 3, the crosses indicate the amplitude measured at each sample time, and the dotted line shows the waveform generated by sampling. This graph shows the resulting waveform generated using a low sample rate.
[This image shows the same information as Fig 4, but using a low sample rate[Image:wave7.gif]]
[Fig 7. An amplitude/time graph showing the sampled waveform. This waveform was generated at a low sample rate, and therefore the resulting waveform is much more coarse compared to Fig 4. Notice that although the general shape is similar to the original waveform, and much of the smoothness is is lost between the time of each measurement. The loss of smoothness also means loss of information since this waveform is not the same as the original. If you compare this graph against Fig 4 then you will see that the lower the sample rate, the more information is lost. The higher the sample rate, the less information is lost. Therefore, to record a sound, it is best to use a high sample rate]