Error Correction Tests

In this section, we try to simulate one of the most interesting problems an average user frequently faces while using a DVD player, namely the reading accuracy of a DVD player when accessing a defective or scratched DVD or CD. The performance of the drive here may be influenced by the quality/precision of its mechanical parts (Optical Pickup Unit, sufficient servo control, etc), as well as with the drive's reading strategy under abnormal conditions, controlled by the main chipset and firmware commands. We tested the Pioneer DVR-320-S with a number of pressed DVD-Video and AudioCD test discs. The ABEX series from Almedio offers a good picture of a CD/DVD reader's error correction capabilities. In addition, we used the SBC444A test disc from Philips and CD-Check test disc from Digital Recordings.

DVD-Video

• Abex TCD-545

This is a single-sided, dual layer (S-2 type, OTP) disc with 8.5GB capacity. The disc can be used for checking the layer switching operation from layer1 to layer 0. The disc also includes test pictures and test signals for Dolby Digital, linear PCM (48kHz/24bit, 96kHz/24bit) and others, to examine high quality pictures and sound. The disc content is an MPEG-2 NTSC DVD-Video file. The TCD-545 includes defects on the disc area (black dots and fingerprints). The size of the black dots varies from 0.4mm to 1.0mm and fingerprints from 0.065mm to 0.075mm.

The DVR-320-S read the disc successfully without skips, picture stills or glitches being noticed. This good behavior is also prominent amongst most PC DVD recorders/players. Now, we shall proceed to the next test disc, the Abex TCD-541.

• Abex TCD-541

This disc is exactly the same as the Abex TCD-545 tested previously, except that the defect is a scratch ranging in size from 0.4mm to 3.0mm, increasing by 0.2mm /per step. The DVR-320-S showed very good performance again. All chapters of the DVD-Video were played correctly. Here we should say that not all PC DVD/CD players are able to read this specific type of disc.

AudioCD

• Abex TCD-726

This is an AudioCD disc used for measurement and adjustment of the error correction capability and tracking/focusing servo characteristics of a player against possible defects on some CDs. Three kinds of defects are included on this disc, :interruption in information layer, black dots and fingerprints. The interruptions are fabricated by intentionally varying the lengths of pits in the disc fabrication area. Their size varies from 0.5mm to 1.0mm. The diameter of black dots is from 0.4mm to 1.0mm. The simulated fingerprints are, in turn, small gathered dots, of diameters sized from 65 micrometers to 75 micrometers. 160 black dots together construct an artificial fingerprint.

All audio tracks were played on the DVR-320-S. No audible read errors (clicks, skips) were noticed.

• Philips SBC 444A

The test concept with the Philips SBC 44A is the same as in the previous test disc. Interruptions on the information layer vary from 400 micrometers to 1000 micrometers, while black dots have size of 300 micrometers to 800 micrometers. Once again the DVR-320-S read the contents of the disc without any problems.

• Abex TCD-721R

The medium has the same contents as the Abex TCD-726, but a different defect- a scratch sized of 0.4mm to 3.0mm on the disc's surface. Error symptoms expected when playing this disc are noise, sound skips, same sector repeatedly played, start of tune cannot be detected, etc.

The DVR-320-S played successfully all 15 tracks. Such behavior is a sign of strong error correction/concealment capabilities.

• CD-Check

We finish this testing cycle with the CD-Check disc from Digital Recordings. Five audio signals (5 tracks) are combined with disc error patterns to rate the player's ability to read and reproduce music completely. The five tracks contain a sequence of tests of progressively rising difficulty .

Check level 1 (track 1): Standard manufacturing errors

Check level 2 (track 2): 0.375mm scratch

Check level 3 (track 3): 0.750mm scratch

Check level 4 (track 4): 1.125mm scratch

Check level 5 (track 5): 1.500mm scratch

Any clicks, interruptions or looping during audio reproduction indicate failure of a Check level (audio track). Below you can see the test results:

The DVR-320-S played flawlessly the first 2 tracks, which correspond to a scratch up to approximately 0.750mm, at the end of the track. Notice that the same player managed to correct more seriously defective areas on the Abex TCD-721R test disc (up to 1.8mm). The explanation here must be related to the way the scratched areas are positioned on the surface of each disc. The Abex TCD-721R places the scratched area on a single part of the disc. On the other hand, the CD-Check disc "slices" the disc circle in four equal sectors and each scratch is placed along the margins of each sector (four equal scratches on the disc).

As a result, the drive "faces" the same scratch 4 times per cycle, making playback more difficult. You should bear in mind however, that error correction/ concealment procedures may be affected by statistical factors, and thus, repeating the same test does not always give exactly the same results.

Summarizing, we can say that the DVR-320-S performed well in our error correction tests, even though its performance on the last test could be better. We've seen most DVD players getting through track 3 without any problems. We've even seen lately, DVD players coming from less well known manufacturers that can go through all 5 tracks with 1-2 glitches in the last track.