Clive's FAQ About Audio on a PC
Page last updated: 19th April 2000
This page is a response to the fact that I tend to get a lot of emails asking for advice on a variety of issues related to audio on a PC. If you are thinking of emailing me with a question, please check first to see if it's answered here.
Before we start, here is a list of subjects that I often get asked about, but of which I have little or no knowledge:
· CD-Text
· Restoration of old 78rpm records
· Audio on a Mac
· MP3. [This is a subject which has no relevance for me at present. I work exclusively with WAV files and standard audio format CDRs. However, here is a page about MP3 written by somebody who is clearly very enthusiastic. It seems to have a great deal of useful information, although of course as somebody who knows very little about MP3 I can't comment on it's accuracy. I will point out one slight reservation I have about the page: it seems to me that the author sometimes takes a rather black-and-white view of some things; there is a sense that he often says, "these are the facts, there is no room for debate". I generally prefer to remain less prescriptive, even in areas where I do hold strong opinions.]
Contents
· How do I record from cassette tape to hard disk?
· I can play through the computer speakers, but can't record to hard disk
· I'm getting dropouts during recording to hard disk
· When I record to hard disk I'm only getting one channel
· How do I burn an audio CD with multiple tracks but no gaps between the tracks?
· How do I create a CD with "countdowns" between tracks?
· How do I put "hidden" music before the first track on a CD?
· What's the format of a WAV file?
How do I record from cassette tape to hard disk?
1. Connect the output of the cassette deck to the line input (NOT the mic input) of the soundcard.
You will probably need a cable with two phono plugs on one end and a stereo mini-jack on the other. Phono plugs (also known as RCA plugs or Cinch plugs) have a thin centre pin and a surrounding ring about 1/4" (6mm) diameter. Stereo mini-jacks look like the plug on a pair of headphones used with a Walkman. Most audio stores sell cables like this; they are primarily designed to connect the output of a Walkman into a home stereo system.
2. Bring up the Windows Volume Control utility, select the Recording screen, and make sure the line input is selected. For a more detailed discussion of the Volume Control utility, see here.
3. Use a suitable hard disk recording package (such as CoolEdit, GoldWave, etc) to record. Use the slider on the Volume Control utility's Recording screen to adjust the record level. Some hard disk recording packages may have their own record level slider, in which case it might be more convenient to use that.
If you intend to write the results to a CDR, use WAV format, 16bit, stereo, 44.1kHz. Some recording packages describe this as "CD Quality".
I can play through the computer speakers, but can't record to hard disk
There is a difference between which inputs are made available to the soundcard's output, and which one is made available for recording.
Open up the Windows Volume Control utility. (This is usually available by double-clicking the little yellow icon of a loudspeaker in the system tray. If it's not there, go via Start|Programs|Accessories|Multimedia, or perhaps Start|Progams|Accessories|Entertainment). A screen titled "Volume Control" appears. On this screen you will see a selection of inputs. Each one can be individually switched on or off using its "mute" checkbox. All those which are not muted are available for playback through the soundcard's output, and their relative volumes can be controlled using the appropriate sliders. Thus, this screen behaves like a simple mixer, allowing multiple sources to be gathered together for output.
OK, all this is fine, and allows you to pass the input through to the output, but: it doesn't make the unmuted inputs available for recording to hard disk. To do this, select the "Properties" item from the "Options" menu. A screen titled "Properties" will appear. In the box titled "Adjust volume for", there are radio buttons: select the one for Recording. A list of available inputs appears in the box beneath "Show the following volume controls", and you should ensure that all the various inputs you may wish to record are checked in that list. Now press "OK", and the main screen's title changes to "Recording Control". This screen presents the inputs available for recording, and to activate the one you want, check its associated "Select" checkbox. The recording level can be adjusted using the selected input's volume slider. Note that you can adjust the record level while recording, and there is a simple meter next to the slider that gives you some idea of the level. However, this meter is uncalibrated and most hard disk recording packages are likely to have better metering. Once you have set the required record level, you can close down the Volume Control utility and the settings will remain unchanged.
One further tip. If you're recording anything other than the microphone input, it is a good idea to mute the microphone on the "Volume Control" screen whilst recording, as the microphone input circuitry can add a fair bit of noise on many soundcards.
I'm getting dropouts during recording to hard disk
There are a host of possible reasons for anomolies during recording. Most of them are system configuration issues, and they are discussed here in the order that you should investigate them, not necessarily because the earlier ones are more likely to be the cause, but because they are easier to check and/or correct. Remember that after making any Windows system configuration changes it is necessary to reboot the PC before they take effect.
1. Compressed Hard Disks.
There is nothing that can be said about this except: don't try to use compressed hard disk partitions for digital audio.
2. Rogue Video Card Behaviour.
Some video cards, especially those which perform Windows acceleration, obtain a small performance boost by not bothering to check if the bus is free before attempting to use it. The result of this is that, if the bus isn't free, then the video card tries to use it and blocks the bus, resulting in audio samples getting lost.
A temporary solution might result from turning down the level of graphics acceleration (in Win95/98, via My Computer | Properties | Performance | Graphics).
The proper solution is to contact the video card manufacturer and find out whether there is a way to configure its driver so that it always checks that the bus is free before using it.
3. FindFast and Other Background Tasks.
Programs lurking in the background which might spring into life at inappropriate moments are to be avoided. Things such as screen savers, email servers and the like should be switched off. One particular program of this type is FindFast; if you have installed a recent version of Microsoft Office it is probably on your system. The problem with FindFast is that you never really know it's there unless you take the trouble to check what tasks are running. If you discover that it is running, kill it, and also remove it from the Programs Menu Startup group (where it is likely to have placed itself).
4. File System Read-Ahead.
By default the Windows file system reads ahead, on the assumption that the running program is soon likely to want the data that follows. This is all very well for a typical PC performing a general mixture of "normal" computer activity. It is, however, the last thing you need while you're recording audio. Try reducing the amount of file system read-ahead (via My Computer | Properties | Performance | File System).
5. Recording Software Buffering.
If your recording software has facilities to adjust the buffering it uses then it is worth experimenting with that. Some packages have a default buffering strategy that is quite miserly. It costs nothing to increase but a little memory, and most modern systems have plenty to spare.
6. 32-bit Disk Drivers.
I know of one person who had a problem with a continuous "ticking" type of dropout during recording. He cured it by disabling 32-bit protected mode disk drivers. You can do this via My Computer | Properties | Performance | File System | Troubleshooting.
7. System vcache Settings.
The Windows virtual cache is quite often the culprit when occasional (rather than constant) dropouts are experienced. That said, it is probably better to eliminate other possibilities first, since to adjust the vcache requires that you edit the SYSTEM.INI file rather than just adjust some settings.
If the vcache is allowed to change in size, it'll be just your luck that it does so in the middle of an important recording, with a consequent loss of samples. The trick is to set the vcache up with the same settings for its minimum and maximum size, thereby stopping Windows ever resizing it. To do this, you need to edit the file SYSTEM.INI in the Windows system directory (usually C:\WINDOWS). Open the file with any text editor (eg. Notepad) and find the section headed [vcache]. Add two lines beneath, so that the section looks like this:
[vcache]
MinFileCache=4096
MaxFileCache=4096
If there is no [vcache] section, add one at the bottom of the file. If the existing [vcache] section already has settings for MinFileCache and MaxFileCache, adjust them accordingly. The actual value to use (4096 in the example above) is the size in kilobytes of the cache. 4096 (ie. 4MB) is appropriate for a PC with about 32MB of main RAM. Generally about 1/8th of the main RAM is a suitable amount to use, but if you have more than 64MB of main RAM, it probably isn't worth setting your vcache above 8192.
8. IRQ Conflicts.
If your soundcard attempts to use the same IRQ as another device, anything can happen. If all your devices are plug-and-play, it is easy to check that there are no conflicts by going through each device under My Computer | Properties | Device Manager. If you have any non-plug-and-play cards, they must be set up manually to avoid conflicts. Moreover, you must also instruct the BIOS to prevent allowing the IRQs used by those non-plug-and-play cards to be assigned to plug-and-play cards. To do this, it is necessary to enter the BIOS setup during PC bootup, find the place where IRQ assignments are made, and set those IRQs being used by non-plug-and-play cards to the appropriate value (often called something like "ISA", or "N/A", or "Legacy").
9. Soundcard Drivers.
Although unlikely, it is possible that the drivers for your soundcard have some kind of incompatibility with the timing of your main system board. Modern PCs are less likely to have this problem; it was more an issue with old ISA bus 386 and 486 machines. Nevertheless, you should make sure you have the latest drivers for your soundcard.
10. Disk Fragmentation.
In these days of Ultra-ATA and SCSI hard disks, fragmentation is rarely an issue. Modern hard disks are so fast that the data rates required by simple stereo audio is no problem unless there is an extreme degree of fragmentation. However, occasionally defragmenting your hard drive can't hurt, so it's worth doing it now and again.
When I record to hard disk I'm only getting one channel
This is most often caused by using a mono minijack. A soundcard's line input is a stereo minijack socket. It is easy to recognise the difference between mono and stereo minijacks: a mono minijack has one thin plastic ring near the tip of the connector, whereas a stereo one has two plastic rings.
The other possibility is that you have accidentally plugged into the soundcard's microphone input (most mic inputs are mono), although in most cases feeding a line level signal into a mic input causes serious overload distortion.
How do I burn an audio CD with multiple tracks but no gaps between the tracks?
There are two basic ways to burn an audio CD. These are known as "Track at Once" (TAO) and "Disc at Once" (DAO).
When a CD is burned in TAO mode, the laser is switched off between each track, and by default this causes a gap (usually 2 seconds) between the tracks. Some CDR drives allow this gap to be adjusted, and some CDR writing software allows you to set the gap if the hardware supports it. In extreme cases it may be possible to set to inter-track gap to 0. Whether this achieves what you want depends on the hardware's ability to pick up precisely where it left off, and in most cases even with a gap of 0, there will be a tiny but noticable "tick" between the tracks.
To get the desired effect of multiple tracks with no gap whatsoever between them, it is usually necessary (and certainly more reliable) to burn the CD in DAO mode. Here, the entire CD is written in one go, without the laser being turned off at any stage. The disadvantage of doing it this way is that you can't build up your CDR in steps; you have to have all the tracks prepared and ready on hard disk so the whole disk can be written.
There are two ways to get the track positions in the right place when burning in DAO mode. Which one you need to use depends on the way your CDR writing software works:
1. Some software requires that each track be in a separate WAV file. The best known package like this is Adaptec Easy CD Creator. If you have a single large WAV file containing many tracks, it will need to be split into multiple WAV files. It is important that these splits are made on CD block boundaries (a CD block is 1/75th second, ie. 588 samples), otherwise they will be padded out to the next block size by the writing software. Two suitable packages which can split WAV files on block boundaries are CD Wave and Wave Repair.