Notes: PCR, Pamela Basic, Standard, Professional and Business record in MP3 natively. If you have questions about the sound quality options click here.

Encoding

Encoding is the process of converting uncompressed digital audio into a compressed format such as MP3. When you play the encoded file, it must first be decoded before being processed by the D/A converter in your sound card or portable player.

When encoding, there are more parameters that affect the file size and sound quality. The goal of encoding is to create files with the best possible sound quality, given the constraints of file size or available bandwidth.

Encoding is a game of trade-offs between speed, file size and sound quality. MPEG provides programmers with a lot of flexibility as to how they implement a particular standard. The result is that there can be substantial differences in sound quality between different encoders, even for files encoded at the same bit-rate. The differences between encoders are usually more apparent in the sound quality they achieve at lower bit-rates. At higher bit-rates (above 256 kbps), it’s difficult to tell the difference between encoders.

Bit-rates

The term bit-rate refers to how many bits (1s and 0s) are used each second to represent a digital signal, and the bit-rate correlates directly to the size and sound quality of an MP3 file. MP3 files can be encoded at anywhere from 8 kbps to 320 kbps. Lower bit-rates result in smaller files, with reduced sound quality, and higher bit-rates result in better sound quality, but larger files. Below the formula is shown for calculating the file size for four minutes (240 seconds) of audio encoded at 128 kbps.

Calculating file sizes for encoded audio

(Bit-rate x Length) / (Bits/Byte x 1KB) /1024 = File Size

Example:

(128.000 x 240) / (8 x 1024) /1024 = 3.8MB

Sound Quality

Because sound quality is subjective and varies depending on the encoding program, the bit-rate required to obtain a certain quality level will vary. At higher bit-rates (193 kbps+) on typical home stereo systems, many people will not be able to tell the difference between the encoded file and the original (although audiophiles with good ears and expensive systems often can).

Table 1 - Comparable Sound Quality for MP3 at different bit-rates

MP3 at 128 kbps is sometimes referred to as CD-quality. However, there are so many other factors, such as the type of music and the encoding algorithm that affect sound quality, it’s best not to infer that a specific bit-rate is equal to a certain quality level.

Lower bit-rates may produce files that sound fine with your present stereo system, but someday you may own a higher-end system where you can tell the difference. It’s less work to use higher rates now than to have to recreate the files at a later date. Lower rates do make sense for music intended for a portable player like the Rio (where storage space is at a premium) or for voice recordings (where high frequency response is less critical).

Optimal bit-rate settings

Even though the optimum bit-rate depends on many factors, the generalizations below will help you better understand the options. Advanced users should experiment with different rates to find what works best for them.

With MP3, fair quality sound can usually be achieved with a bit rate set at 128 kbps. If you want to decrease file size even further you may try 64 kbps which will still provide good quality when recording a Skype call. Note that Pamela by default only offers 24 and 32 bit settings. These are the only two options that Windows by default offers. To increase the options you may install the ACM LAME codec. Click here for details and download.

Table 2 - Bit-rates vs. capacity