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Home > Hardware Reviews > Optical Storage

Monday, September 20, 2010
Samsung SH-B123L review

3. Reading of defected CDs

This series of tests checks the drive's ability to correct/conceal possible erroneous data after reading artificially scratched / defective audio discs.

Using a CD-R in best shape to do the DAE test is generally not a safe way to test the drive's error correction capabilities. If your drive would not read audio CDs error free from an error free disc, you would probably bring the drive back to the vendor. It is far more interesting to see how a drive is behaving under critical conditions (which will also tell something about the DAE quality on CDs that have manipulated C2 error information on purpose). For that a special test CD like the ABEX discs from ALMEDIO can be used, that can be used to do a comparison between different drives. The ABEX test disc is actually an AudioCD that has artificial scratches and other physical disc error patterns on its surface.

Using a special software, we compare two audio files using FFT analysis. The first audio file has been extracted by a normal audio disc without physical error patterns on it . The second one is the result of the extraction of the ABEX test discs which hold the same audio tracks, but it also has specific defects on its surface. The similarity factor of the the two tracks unveils the error correction capabilities of the drive.

The differences between the two compared tracks are translated to a signal (noise) illustrated in the following graphs. Each graph tells a lot about the abilities of the drive. The quality of the optical system (and/or of the error correction capabilities of the firmware) is shown in at which time index the error start. The error hiding qualities are shown when the wedge gets bigger. For example, a drive that will start error correction quite early indicates either bad optics and error correction. However, if the corrected data (wedges) stay below -60 dB(A) , this means that the drive has sufficiently hidden these errors and they most probably be unaudible, especially if they are surrounded by loud music.

The X position of a grid line is always a start of a new minute position on the CD (in play time, up to 74 min). The Y axis shows the dB(A) value of the error in the extracted file. The 0 dB(A) baseline at the top is marked slightly different. So the graph shows a range of 6 dB(A) down to -120.0 dB(A). Each line represents 6 dB(A) of volume (6 dB(A) louder means that the sound is double as loud).

- ABEX TCD-721R

 

Errors total Num : 1141062
Errors (Loudness) Num: 56849 Avg: -73.5 dB(A) Max: -12.3 dB(A)
Error Muting Num: 3637 Avg: 1.0 Samples Max: 18 Samples
Skips Num: 0 Avg: 0.0 Samples Max: 0 Samples
Total Test Result 76.5 points (out of 100.0 maximum )

The Samsung SH-B123L drive muted many faulty samples. The average value for the errors is not high , although some wedges are high (max -12.3 dB(A)). This means that some distortion (clicks, pops) could reach your speakers in the specific areas if you playback this file. No skips were reported, meaning that the sync was not lost forcing the drive to reposition again.

This is an average performance for the drive, compared to the results we have seen from other DVD and BD burners.

- ABEX TCD-726R

Errors total Num : 0
Errors (Loudness) Num : 0 Avg : -174 dB(A) Max : -174 dB(A)
Error Muting Num : 0 Avg : 0.0 Samples Max : 0 Samples
Skips Num :0 Avg : 0.0 Samples Max 0 Samples
Total Test Result 100 points (out of 100.0 maximum)

It seems that the defects on the surface of the specific disc were not enough to make the drive lose track. Both extracted files ("norma"l and "damaged") were almost similar, meaning that the drive is very capable of correcting any kind of errors caused by the specific defects (fingerprint, dots).

these errors.

- CD-Check Audio Test Disc

CD players have built-in D/A converters that turn the digital data on a CD into analog signal - what we hear as music. Ideally, all the digital data should be converted to the analog format. In reality, many factors cause digital data to be lost and sound reproduction to detoriate.

CD players handle this data loss using a sophisticated error correction system that allows them to recover it. However, when the data loss is greater than a system;s recovery ability, some of the signal is lost. It is then that the CD player uses compensation methods such as interpolation, data substitution or signal muting to make this loss as anaudible as possible. However, this results in altered and often distorted sound.

The level of sound distortion depends on the amount of data loss. Initially, music may sound brittle and there may be subtle problems with stereo imaging or dynamics. Over time, disc skipping, clicks, pops in the signal or audible signal muting may result. CD-CHECK contains a special signal (tone), designed for early detection of the most subtle forms of distortion. The disc offers a signal combination with disc error patterns to rate the drive's abilities to read music and reproduce it completely. Five tracks on the disc contain a sequence of progressively more difficult tests. These tracks are referred to as Check Level-1 through Check Level-5.

The tracks are reproduced through a software multimedia player (e.g. Windows Media Player). Each level is considered as passed, if the tone is smooth, continuous without interruptions, skipping or looping. The higher the Check Level passed, the more reliable the sound reproduction of the tested drive.

Error Level 1 2 3 4 5
Samsung SH-B123L 5/5 5/5 5/5 5/5 4/5

As it was expected, the error hiding mechanism of the Samsung SH-B123L drive as well as the drive's tend to mute faulty samples resulted to a flawless reproduction of all the first four tracks of this test disc, and and a very good result in the 5th track (harder), which was correctly reproduced 4 times out of the 5 we tried in total.




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