User's Manual

BrailleNote Apex BT User Guide
17-410
17.2.6 Sampling Frequency.
The sounds we use and hear in the real world, such as our voices, are "analog" signals. This means
that they are continuous and constant. To process these signals as a recording, we need to convert
the signals to "digital" form. Digital signals are not continuous, and so to create the effect of
continuous sound, a process called sampling is used. The value of the signal is measured at certain
intervals in time, and each measurement is referred to as a sample.
The frequency with which samples are measured is called the sample frequency. The more samples
that occur in a second, the better the quality of the sound. As the measurement used to describe this
is Kilohertz or kHz, the larger the number of kHz, the better quality the sound.
Of course, the higher the sample frequency, the larger the resulting file will be. Because there will
be times when the sound quality is not as important to you as the amount of storage space you have
available, the Recorder has three sample frequencies to choose from: 11.025 kHz (low quality),
22.05 kHz (medium quality), and 44.1 kHz (high quality). The factory default frequency is
22.05kHz.
17.2.7 Bit depth.
A bit (short for binary digit) is the smallest unit of data in a computer. The range of a digital signal
is measured in bits. So, each time a sample is taken, the size of that sample is measured in bits. This
is called a bit depth, because the size of the sample is determined by the vertical range of the sound
wave
The Recorder has two available bit depths - 8 bits and 16 bits. Using 16 bits per sample gives a
higher quality recording with a larger dynamic range and less noise. However, it uses twice as much
storage space as 8 bits. The factory default bit depth is 8 bits.
17.2.8 File size.
As discussed before, the higher the sample frequency and bit depth of a recording, the larger the
resulting sound file will be. However, the larger the file, the better the sound quality. Therefore you
may want to make a value judgment about what to record at a high quality and what to record at
lower quality, to manage your storage capacity. Below is a breakdown of the relative sizes for 10
second and 60 second sound recordings according to the sound quality.
For a 10 second recording, the file sizes are:
1. Low Frequency sample, Low quality bit depth =107KB
2. Medium Frequency sample, Low quality bit depth =215 KB
3. High Frequency sample, Low quality bit depth =431 KB
4. Low Frequency sample, High quality bit depth =215 KB