Browse Prior Art Database

Method for Preventing Audio Distortion in Sequential Digital Audio Read Operations

IP.com Disclosure Number: IPCOM000112053D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 102K

Publishing Venue

IBM

Related People

Desai, DM: AUTHOR [+5]

Abstract

Disclosed is a method for performing SCSI read commands to a Compact Disc-Digital Audio (CD-DA) drive to retrieve data without time distortion. While such a drive has only approximate addressing for each sector, using this method, audio information read from a disc is marked by a control algorithm as it is stored in a drive buffer. Sequential read requests are serviced according to these markings, avoiding a need to find a new sector by means of an inexact process. In this way, sectors may be sequentially read from the disc with exact relative addressing of each sector, for playback without distortion.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method for Preventing Audio Distortion in Sequential Digital Audio
Read Operations

      Disclosed is a method for performing SCSI read commands to a
Compact Disc-Digital Audio (CD-DA) drive to retrieve data without
time distortion.  While such a drive has only approximate addressing
for each sector, using this method, audio information read from a
disc is marked by a control algorithm as it is stored in a drive
buffer.  Sequential read requests are serviced according to these
markings, avoiding a need to find a new sector by means of an inexact
process.  In this way, sectors may be sequentially read from the disc
with exact relative addressing of each sector, for playback without
distortion.

      CD-DA discs do not allow direct and exact sector addressing,
due to the method used for recording the data comprising a sector and
the method used for recording a corresponding time stamp for the
sector on the disc.  The data is recorded on the main channel, while
the time stamp is recorded on a sub-channel.  The sectors can be
addressed only by means of the time stamp, but conventional
technology for both disc mastering (recording) and playback does not
provide for an exact correspondence in time between each sector and
the corresponding time stamp in the sub-channel.  These signals
cannot be kept aligned in time due to differing slew times in the
paths to record and playback the main channel and the sub-channel.
Also, on some discs the sub-channel is periodically used for other
purposes, removing the time stamp altogether.

      For example, a controlling program may begin reading from the
disc at sector m, reading n sectors sequentially at a time.  In the
first read operation, the error is  75 sectors, which does not
cause a problem, as the audio data does not have to start on an
absolute address.  However, subsequent read operations should begin
precisely at  sectors from the previous read operation to prevent
time distortion of the audio data.

      A control algorithm is employed within a compact disc drive for
retrieving data from the disc, allowing the data to be accessed
through the SCSI bus interface.  In CD-ROM operations (i.e.,
operations reading information data, not audio data) the control
algorithm continually retrieves sectors from the disc, starting at
the point to which it is directed by the read command sent from the
SCSI interface.  The algorithm reads more data than requested until
the entire drive internal buffer is filled.  For example, the
internal buffer may have a capacity of 64KB, which translates into
approximately 27 sectors of data, with each sector containing 2048
bytes of data and 304 bytes of control, error detection, and error
correction information.  When the cont...