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Home > Hardware Reviews > Optical Storage

Friday, April 08, 2011
Sony BWU-500S Review

3. CD Error Correction tests

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. 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: 886400
Errors (Loudness) Num: 48947 Avg: -74.0 dB(A) Max: -36.3 dB(A)
Error Muting Num: 2939 Avg: 1,1 Samples Max: 18 Samples
Skips Num: 0 Avg: 0.0 Samples Max: 0 Samples
Total result C2 Accuracy: 99.7 %
76.9 points (of 100.0 maximum)

The drive's error correction is good, starting at the point where the defect is starting to grow, but error hiding mechanisms are average. We can tell that by the noise that almost all the time exceeds that -60 db(A) level, especially around the 32min mark where the scratch on the surface of the disc becomes bigger.

- ABEX TCD-726R

Errors total Num: 0
Errors (Loudness) Num: 0 Avg: -174.0 dB(A) Max: 0 dB(A)
Error Muting Num: 0 Avg: 0 Samples Max: 0 Samples
Skips Num: 0 Avg: 0.0 Samples Max: 0 Samples
Total result 100 points (of 100.0 maximum)

This time the Sony drive did it pretty well with the ABEX 726 test disc. All the errors seems to have been corrected.

- Nero DiscSpeed - Advanced DAE Error Correction Test

Nero DiscSpeed's Error test determines the capability of a optical drive to prevent errors when creating a copy. The test is run in two steps: The 'Create Image' feature first creates an image file of a test disc and saves it on the hard drive. We extracted data from an A-BEX disc in order to create an error-free image file on the hard drive. After this, the 'Run Test' feature reads the data on the ABEX TDC-721R and TCD -726 test discs in order to compare it with the image file.
the same disc.

To run this test we used a standard test disc of the type A-BEX (TCD-714R, TCD-721R, or TCD-726). All A-BEX discs contain the same data (audio data). The reading surface of the various A-BEX discs contains a series of intentional defects of varying severity.

  • ABEX TCD-721R

This results makes sense only if you compare the score of two or more drives. Here we don't have any comparison data so we may just comment on the amount of C2 errors and those which were missed. Both these figures were expected to be high since the TCD 721R disc features a very wide artificial scratch on its surface. Hopefully, no sync errors were reported. Synchronization errors occur when data is correct but has been moved by one or more sectors.

The reported C2 accuracy (83.75%) for the Sony drive was determined based on the results of the test.

  • ABEX TCD-726

As we previously saw, the TCD-726 disc was easier for the drive to read and no errors were reported.

- 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
Sony BWU-500S
5/5
5/5
5/5
5/5
2/5

 

A good performance for the Sony drive , as it successfully played the first 4 tracks and also managed to correctly play the fifth track (heavily damaged area) two times.

Summary

Generally the drive showed great error correction capabilities even with heavily scratched media, which was mainly unveiled in the CD Check test. The drive successfully read the data of the TCD -726 disc and managed to correct any read errors.




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