78 lines
5.3 KiB
HTML
78 lines
5.3 KiB
HTML
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<TITLE>The Linux MP3-HOWTO : Hardware Requirements & Performance Issues.</TITLE>
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<H2><A NAME="s6">6. Hardware Requirements & Performance Issues.</A></H2>
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<P>Digital Audio processing is a resource intensive task that relies heavily on
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the processing and I/O capabilities of a system. I would strongly recommend
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a Pentium class machine as a minimum.
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<P>If you are going to be encoding from an analogue audio source via the line or microphone input, a PCI soundcard will give the best results. The I/O performance difference between an ISA and PCI based card is significant, over 132 MBytes/sec for PCI (quote taken from the <EM>PCI-HOWTO</EM>). Naturally, the better the quality of the soundcard in terms of its signal-to-noise ratio, the better the encoded MP3. I've been using the Soundblaster PCI128 and just switched over to a Soundblaster Live Value; both cards give good audio performance, but the Live has significantly better S/N ratios, good enough for semi-pro audio work. Remember the old data processing maxim:- garbage in - garbage out!
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<P>Creative have a Beta driver for the Soundblaster Live! which can be
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downloaded from:
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<P>
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<A HREF="http://developer.soundblaster.com/linux/">http://developer.soundblaster.com/linux/</A><P>When recording analogue audio to a hard disk, more commonly referred to as
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direct to disk or d2d recording, the performance of the disk, and its
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interface is critical. If you are using an IDE based based system, mode 4
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or UDMA is preferable as the transfer rate is sufficiently high enough to provide reliable data transfer without problems.
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<P>The ideal solution would be to use a SCSI based system as the drives and
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interface have far better throughput capabilities, a sustained 5MB/sec
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for SCSI 1 through to 40-80MB/sec for ultra-ultra2/wide SCSI. IDE can peak at
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anything from 8.3 MB/s to 66 MB/s for Ultra DMA mode 4 but these speeds are peak,
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average transfer rates will be slower. If you can find, or afford, an AV
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SCSI drive, go for it. AV drives have had the read/write head system optimised for continuous data transference; other SCSI and IDE drives normally cannot sustain continuous data transfer as the write head heats up!
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<P>Naturally a drive that has cache will give more consistent results than one that
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doesn't, as the cache will act as a buffer if the heads do lift or it cannot
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handle the throughput.
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<P>If your drive isn't up to spec, your recording will suffer from dropouts and
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glitches, where the drive failed to record the signal. If you are recording
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one-off events, such as live performances invest in a good SCSI based disk
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system.
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<P>Another cause of d2d dropouts is a heavily loaded system. Background tasks
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can cause the system to momentarily glitch. Its recommended to run as few
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background services as you can, especially networked based services. For
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more information about setting network services, and startup scripts please
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refer to the <EM>SAG</EM> and <EM>NAG</EM> guides.
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<P>Virtual memory paging will also cause glitches, so run with as much physical
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RAM as you can, I'd recommend at least 32 Mb, but you may well need more.
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<P>For those wanting to extract the most out of their system, optimising the
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kernel probably wouldn't do any harm either.
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<P>For streaming MP3's the better the network card the better the throughput, naturally a 100Mb interface will give better throughput than a 10Mb interface :)
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<P>While the hardware specifications above will give you a decent system to
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encode audio data, don't discount using older, lower spec kit if that's all
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you have access to.
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<P>It'll be a good challenge for a sys-admin to tweak a low-spec system to
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give good results, and the end result will probably be a happier Linux box.
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<P>Another important issue is the audio cabling. Cheap, poor quality cables
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and connectors will result in poor recording quality. If your soundcard has
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the option to use phono, sometimes referred to as RCA connectors, use them.
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Gold plated contacts will also help maintain audio quality, as will keeping
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audio cables away from data cables as there will be a chance of interference
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between them.
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<P>But don't forget, spending a fortune on the best audio cabling will be lost
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if the rest of the system hasn't been optimised.
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<P>For encoding MP3's from CD-ROM, the speed or type of drive will determine the
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time taken to read the raw information from it. A single speed drive will
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probably be too slow for all but the most patient.
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<P>Your CD-ROM must be connected to your soundcard if you want to hear what you
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are recording, either using the internal connector or by connecting headphone's to the headphone output, although you will not be able to listen to MP3's through the CD-ROM headphone socket!
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<P>For detailed instructions on setting up soundcards, now would be an excellent
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time to read the <EM>Sound-HOWTO</EM>.
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<P>
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