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This page explains briefly the digital audio related topics. further information please contact support@amazing-online.com

4. FAQ

44100 Hz means that you have 44100 values per second coming in from your the CD-ROM (or input file). Multiply that by two, because you have two channels. Multiply by another factor of two because you have two bytes per sample (i.e. 16 bits per sample). The song will take up 44100 samples/s x 2 channels x 2 -bytes/sample ?60 seconds/min Mbytes (is about 10 MBytes/min) of storage space on your hard disk.

If you want to download that over the Internet, given an average 28.8 modem, it would take you about 10,000,000 bytes x 8 bits/byte / (28800 bits/s) x / (60 s/min) or about 45 minutes. Just to download one minute of music!

Digital audio coding, which - in this context - is synonymously called digital audio compression as well, is the art of minimizing storage space (or channel bandwidth) requirements for audio data. Modern perceptual audio coding techniques (like MPEG, Vorbis, AAC ) exploit the properties of the human ear (the perception of sound) to achieve a size reduction by a factor of 12 with little or no perceptible loss of quality.

Therefore, such schemes are the key technology for high quality low bit-rate applications, like soundtracks for CD-ROM games, solid-state sound memories, Internet audio, digital audio broadcasting systems, and the like.

When you deal with compression technology, often you have to specify the "bitrate". The "bitrate refers to the transfer bitrate for which the files are encoded - i.e. an MP3 file encoded "at a bitrate of 128 Kbps" is compressed such that it could be streamed continuously through a link providing a transfer rate of 128 thousand bits per second. But most of us don't really use MP3 as a streaming medium (except for shoutcast, etc.) so really what the MP3 "bitrate" is a measure of is how severely the files is being compressed - the lower the bitrate, the more the file has been compressed... and the more you compress a file. the more of the original data is lost. So in effect the worse the playback sound quality will be.

1) Constant Bitrate (CBR)

This is the default encoding mode, and also the most basic. In this mode, the bitrate will be the same for the entire file. It means that each part of your mp3 file will be using the same number of bits. The musical passage beeing a difficult one to encode or an easy one, the encoder will use the same bitrate, so the quality of your mp3 is variable. Complex parts will be of a lower quality than the easiest ones. The main advantage is that the final files size won't change and can easily be predicted.

2) Average Bitrate (ABR)

In this mode, you choose the encoder will maintain an average bitrate while using higher bitrates for the parts of your music that need more bits. The result will be of higher quality than CBR encoding, and this mode is highly recommended over CBR. This encoding mode is similar to what is reffered as vbr in AAC or Liquid Audio (2 other compression technologies).

3) Variable bitrate (VBR)

In this mode, you choose the desired quality on a sqale from 9 (lowest quality/biggest distortion) to 0 (highest quality/lowest distortion). Then encoder tries to maintain the given quality in the whole file by choosing the optimal number of bits to spend for each part of your music. However, this mode heavily relies on the encoder psychoacoustic model and could lead to a few "bad choices" in the encoding process. You may want to specify a minimum bitrate (e.g.:set to 64 kbps) to avoid those potential errors.

Q: What's an ASPI manager, and how do I know if I have one?
A: ASPI is an interface created by Adaptec, and is used by Amazing MP3 Creator to access the CD-ROM hardware. Windows 95/98 comes with the ASPI manager pre-installed, while NT/2000/XP does not. To tell if you have an ASPI manager installed, look for a file called WNASPI32.DLL in your Windows system directory (c:\windows\system or c:\winnt\system32 are common locations). For NT, it is usually supplied by the manufacturer of your SCSI adapter or devices -- unfortunately, not usually supplied for IDE devices under NT. Some ATAPI CD-R and CD-RW devices do however supply the ASPI manager, specifically so that it can interface with the CD-R and CD-RW burning software.

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Q: Does Amazing MP3 Creator work without an ASPI manager?
A: Under Windows NT (SP 4+) and Windows 2000/XP, Amazing MP3 Creator can use the SCSI pass through interface to gain low-level access to the CD unit. The preferred method is still via the ASPI manager, but since neither Windows 2000 nor NT has a built-in ASPI manager, this method is provided as a fall-back.

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Q: What is "jitter", and just how does "jitter correction" work?
A: "Jitter" is a term used for the inherent uncertaintly in most CD-rom units, which is caused by the way audio is stored on a CD. Although one logical block on a CD takes up 2352 bytes, the amount of data stored in the block varies. For a data block, 2052 bytes are actual data, and the remaining 300 bytes are information used to accurately find the block. For audio, however, all 2352 bytes contain audio data -- there is no positioning information returned in the block read. When CDs first came out, they were used for audio, and it didn't matter if a CD player got within +/- 1/75 of a second of the intended start position. After it started, as long as the player kept reading, it could accurately read the data -- the problem only came about when initially seeking the start position.

"Jitter correction" is the process of trying to compensate for "jitter" in software. Generally, it involves using overlapping reads, and attempting to match the end of one read with the beginning of the next, so that there are no gaps in the data read. These gaps cause clicks and pops in the resulting WAV or MP3 file produced. For instance, the program might begin reading a track at block 1000 and read 27 blocks total. On the next read, it would issue a read command starting at 1024, and would try to match the end of the first read in the beginning of the second read. Once it finds a match, it would cut off the beginning of the second read, and use only the part after the match. In this way, you can eliminate the clicks and pops.

Amazing MP3 Creator has an additional, more sophisticated mode for jitter correction. It will attempt to issue many read commands quickly and buffer the output. When ripping with Amazing MP3 Creator, you can see this happening in the "Read buffer" gauge on the rip dialog -- it will attempt to buffer as much as it can quickly, and then wait for the encoder to process it. When the buffer is almost empty, it starts reading again. It only performs jitter correction after an error is reported by the CD unit. Most drives will read audio correctly as long as the drive doesn't stop reading for too long, and read commands are issued sequentially, ie. the next read starts immediately where the last read left off. Using this method results in a vast speed improvement over brute-force jitter correction.

Most of the time the "On Error" jitter correction mode will produce good results. However, if you still get clicks and pops using this setting, try using the "Always" setting. Some (higher-end) drives support a feature known as "Stream is Accurate" -- this means that consecutive reads are guaranteed to start where the last one left off.

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Q: I can't seem to rip any tracks at all. Help!
A: Try resetting the jitter correction values to their defaults in the CD Options dialong (click on the "Reset" button). If that doesn't work, In the CD Options dialog, try using the "Autodetect" read algorithm. If it still doesn't work, try the others individually. If none of this helps, send an email to support@amazing-online.com with the make and model of your CD rom, operating system (Win95/98/NT/2000/XP), whether it's a SCSI, ATAPI, CD-R, etc. and a description of the problem. It's also possible that your drive simply doesn't support digital audio extraction -- while most SCSI drives support digital audio extraction, not all IDE drives do.

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Q: I can rip, but it seems to rip very slowly.
A: Try checking the "On Error" jitter correction in the "CD-Rom Options" page. This mode is faster than the "Always" setting, and should produce results comparable to "Always".

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Q: I'm still getting clicks and pops in the ripped tracks. What can I do?
A: Go to the CD Options page by selecting the Options->CD-ROM Options. Try using the "Always" setting for jitter correction -- this setting will attempt to correct inaccuracies in the positioning of the read regardless of whether the CD reported an error or not. If you receive errors, try increasing the overlap a little; this will increase the size of the buffer that is used to align the read, and so increases the chances for successful alignment.

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