Digital Dj'ing - Using a Laptop or PC as part of your Mobile Disco

Many Mobile Discos have made the change from a conventional CD or Vinyl based system to a software based one, usually running on either a full sized pc or a laptop. The fundamentals of both systems are largely the same, and so you shouldn't simply be taken in by reading other DJs horror stories about how their laptop overheated during the first dance at a Wedding or how their full sized PCs power supply exploded halfway through a gig. There are pros and cons of using both systems, but largely whether to use a full size pc or a laptop comes down to personal choice, practicality, budget and space, and you'll often find that DJ's criticising the opposite machine, have never actually used the system that they are criticising!. If possible visit a DJ who already uses a system to that which you intend to use yourself, nothing can sell an idea better than actually seeing it in use!, for the record, I have watched Mobile DJ's use both PC's and Laptops to DJ from, and neither, in my opinion, was more reliable or better than the other, so it should only be personal choice, rather than rumour or scaremongering which makes the decision on that score!.

Is running a Mobile Disco from a PC or Laptop reliable?

Anybody who has ever encountered the windows blue screen of death, or worn out the Ctrl+alt+del keys on their keyboard will possibly dread the thought of using such a system as a platform to their DJ'ing!. In essence, a decent dedicated pc or laptop with a clean install, good quality hard drive and a reasonable amount of memory will out preform most typical home pc set ups which may be running several applications at a time, be infiltrated with virus or spyware traces, and have a hard drive and registry full of corrupt enteries and partly uninstalled files.

The key to running a successful software based DJ system, is to buy a dedicated pc / laptop for the task, and to only run the operating system and DJ Software on there, and never allow it to run other applications or even connect to the internet. This way the installation runs and remains clean and largely error free, will rarely have a corrupt file, and won't get infiltrated or bogged down with several other applications. This advice is given by DJ's who have been using software and PC's for many years, and have found this method of DJ'ing to be just as reliable as conventional DJ'ing from CD's.

The advantages of using a Laptop or Pc to DJ

The advantages of converting your material to music files and using a Pc or Laptop to DJ from are many. The first is the most obvious, gone are the days where you are carrying several heavy boxes of CD's around with you, most DJ's CD collections can easily be converted to MP3 and will fit onto a 80gb - 200gb hard drive!. By converting to Software Dj'ing you also rid yourself of that long search through several hundred CD compilations in order to find that elusive requested track that you just know that you have got somewhere!. With most DJ Software, you can type in part or all of the artistes name or song title and find it within seconds!. It really is possible to find and cue up a request within 5 seconds - something which just can't be done easily or quickly with a CD or vinyl collection.

Other advantages of a software based DJ system, include the possibility to create playlists from frequently used tracks, and you could create playlists from all genres, for example a playlist for background music, one for dance music, one for the 70s and one for the end of the night slowies. Of course you can also group the tracks together and catalog them according to Genre which also makes finding tracks from particular era's easier too. Some DJ Software will also allow you to group tracks together which have a similar BPM - a boon for DJ's who mix.

Which DJ Software should I choose?

There are many different brands and types of DJ Software about, again it comes down to personal preference which type you choose. It is always a very good idea to check out reviews and discussions on DJ Forums and if possible to find a DJ who uses a system based on the software which is of interest to you, so you can actually see it in action, in a disco environment.

Some DJ Software comes with a free trial, which enables you to download and install the software on your system and try it for for free for a time limited period (usually 10 - 30 days). Depending on the cost of the software, there can be differing features. Some Dj Software will simply allow you to cue up and play music using 2 "players", others will have more comprehensive features, such as being able to fade between tracks, alter the pitch and tempo controls in a similar manner to conventional CD and Vinyl turntables, some of the more expensive software will even allow you to mix, or add a USB controller which looks and functions like a twin cd controller!, some Software will even mix the tracks for you!.

Remember that a feature is only worthwhile if you have a use for it!. Carefully consider what features you need, and which will be the ones that you will have any use for. It would be pointless buying a Dj Software package which allows you to mix, if you are a mobile dj who rarely has the requirement to beat mix. Most Software in its basic form, also comes with the option to add and install plug ins which give you additional updates and features, so its worth starting with the basic packages and then adding new features if and when you require them!.

My advice at this stage, if you are new to, or considering Software Dj'ing is to download the free trials of the various software which is available, try them for the time limited period, and then buy the one which suits you, and which is the most comfortable to use.

Some dj software titles which are currently popular and well reviewed by Mobile DJ's include OTSDJ, DSSDJ and PCDJ

What type of PC do I need to run my DJ Software package

When you have decided on a software package, it is then time to consider what pc or laptop to use it on. Contrary to rumour, you don't need the latest brand new pc or laptop to successfully run DJ Software from, and neither do you need a huge CPU processor. Most DJ Software will happily run on a pentium 3 processor with 600mhz speed or higher, many of the newer 1.2ghz+ celerons will also flawlessly run DJ software with no problems and without breaking into a sweat. Try and buy as much memory as you can afford, ideally 512mb of memory or a minimum of 256mb for most applications.

How big should I be :o)

A decent sized hard drive is the next consideration. Remember the bigger the hard drive the more individual tracks that you can fit on there. An average music file ripped at 192kbps is around 5mb in size and so a 100gb hard drive should fit around 20,000 tracks on there. However if you increase the quality of the track in MP3 format, then the file size rises also, so a 320kpbs mp3 could be as large as 11mb in size and so the same 100gb capacity would be reduced to holding only around 9000 tracks. Don't forget to factor in space for your operating software, drivers and DJ software when working out hard drive capacity!. You can of course expand your hard drive capacity by fitting external hard drives to USB ports, and these are also reliable. If possible try and use a system which runs USB2.0 or even firewire since these run at faster data speeds than conventional USB1.1 although many Dj's report no issues with hard drives and soundcards run from older 1.1 systems.

Give me Sound!

Using a good quality soundcard is a must!, many laptops and motherboard based sound chips on full sized pc's rarely do justice to sound quality or are designed with full time high quality audio playback in mind. Consider installing a pci sound card in your pc, or investing in a good quality USB external soundcard if you opt to use a laptop. Most 2 channel soundcards will suffice for DJ'ing in most mobile applications, where the audio is mixed between the players on the laptop and the single output is then fed through a pair of "L" and "R" connectors on the soundcard, and then into the mixer or amplifier.

However, if more creativity is required, or the software is to be used for mixing applications or the use of a crossfader between channels on a conventional mixer is likely to be utilised, then you need to buy a 5 channel soundcard. This allows the soundcard to be set up, in a manner which allows one pair of "L" and "R" outputs to be used for "Player 1" on the soundcard and fed into an individual channel on the mixer, and the same for "Player 2" - this allows each software player to have its own fader on the mixer - just like a conventional twin cd player.

What Quality?

Some Dj Software packages come complete with the means to "Rip" a cd. "Ripping" means placing the original Cd into the PC's CDROM and the process of converting the original music on the CD to MP3 Data, which is then stored on the hard drive as an MP3 File. In the case of OTSDJ, the option is also there to convert to a file called OTS, this is a custom files regonised only by the OTSDJ software, however it sounds just as good as MP3 and is also a slightly smaller file size, meaning that more OTS files can be stored on a hard drive when compared to conventional MP3 files.

If you use a DJ software package which does use conventional MP3 files, then you will need to select the quality at which to "rip". This figure is measured in "Kbps" and often ranges from 32kbps and 320kbps. Lower ranges are not recommended for professional use over a PA system since they can sound dull and even distorted. Ideally for professional use, the DJ should be looking at ripping their CD's to Mp3 files at 192kbps or greater.

192kbps is considered reasonable quality, however 320kbps is near cd quality and may be prefered by some Dj's - however on smaller audio systems the difference may be hard to detect. As the quality is increased, so does the file size, and a 320kbps file may be several mb larger than its 192kbps counterpart, it may also take longer to rip an entire CD at 320kbps than at lower rates.

For Dj Software which doesn't have ripping capability, Musicmatch Jukebox may prove to be an alternative for this process,

Are there any disadvantages to being a Digital DJ?

Now the disadvantages!. Obviously the initial cost of buying a PC / Laptop, a good quality soundcard, large hard drive and the Dj Software itself is likely to total far more than buying a conventional CD Player or turntables. It also takes time to "rip" your cd collection to Mp3 and store them on your hard drive. In some jurisdictions it is also illegal to convert original material to MP3 format for digital use without a licence, and this can prove to be expensive, if the Dj is to work on the right side of the law. It is the possible licence requirement that we discuss next.

Do I need a licence to play music from a laptop?

At the time of writing this article, an annual licence is required in Canada and the UK in order to use a PC or laptop to DJ from. In the UK, a further licence and possible royalty payment is also required for the conversion process. Although no fees have yet been advertised (April 2006) these controversal laws are likely to make this form of DJ'ing unattractive when compared to more conventional, and "licence free" alternatives.

Finally, my tips for Software Djing

* Always buy and use a dedicated pc / laptop purely for Dj use, do not be tempted to use the family pc or run other applications on the machine you use to DJ from, and do not allow this machine to connect to the internet. On a pre-used machine, also start from scratch with a format and fresh install of the operating system.

* Use a good quality soundcard, even if you need to upgrade or buy an external USB one

* Always rip the music direct from an original CD at 192kbps quality or higher. 320kbps is advised for higher quality pa systems and is near cd quality. 192kbps is okay for smaller systems used by the Mobile DJ.

* Don't be too concerned about buying the latest top of the range PC to run from. Most Dj Software will happily run from basic P3 600mhz machines, but do check out the minimum requirements on the software authors website.

* Read reviews on the various software packages available. Stick to the features that you will use, since you can always upgrade extras later. Take advantage of the free trials of DJ Software which are available and use the time to find the best software to suit you

* If you choose a full sized PC make sure that it is professionally flightcased - pc's are not designed to be carried around.

* Select a high capacity 100gb - 200gb hard drive from a reputable manufacturer. Where practical and legal always back up your data

* Fit your machine with at least 256mb of memory, and ideally 512mb.

* Check out the legal aspect of converting original music to MP3 and whether a licence is required to operate such a system.

You may freely use this article on your website, blog or forum, provided a working, active link is provided to the full article at http://www.djsite.info/idx/0/028/article/Running-a-Disco-from-a-Laptop-or-PC.html.

Using Filters to Mix Music

Although it's possible to create a decent mix without any filters at all, they are sometimes very useful. In addition they can be used to change the fundamental character of a sound, rather than just boosting or cutting certain regions to make small adjustments. But how do filters really work?

Most mixers are equipped with a filter section which has a bass, mid and high frequency region that you may boost or cut. In many cases there's one knob for the bass, one for the high frequencies (treble) and one or two knobs for the middle region(s).

If the filters have one knob for the bass, one for the treble and two knobs for the mid range then you cannot choose exactly which bass frequencies that should be boosted or attenuated, nor which treble frequencies these knobs should boost or damp.

Instead the bass knob works as a low-pass filter which cuts at a fixed frequency , for example 100 Hz, and then adds or subtracts the result to or from the original sound. The treble knob works like a high-pass filter which cuts at a fixed frequency , for example 10000 Hz, and then adds or subtracts the result to or from the original sound. The mid frequencies can sometimes be adjusted both in terms of which frequency band that should be boosted or attenuated and how much. Or they work on a fixed frequency region, which is neither bass or treble, but somewhere in between.

Pros usually need to sweep not only the mid range frequency, but also the bass and treble frequencies. However, that doesn't necessarily mean your mixing desk (or mixing software) must be equipped with such filters, to work like the pros. You can use external filter modules (or plug-ins), such as equalizers, to achieve the same result.

What newbies often forget is that filters, such as the bass and treble knobs adjust the volume. Yes, the volume. The bass knob, for example, is used to decide how many dB you should boost or cut in the bass region. Moving the knob to the left cuts a certain amount of dB. Moving it to the right boosts a number of dB in the bass region. Thus it boosts or cuts the volume in the bass region.

If you check the marks on the bass knob and move it 6 dB to the right, then you will increase the volume on that track with 6 dB, but only in the bass region. Consequently, filter changes result in volume changes, but only in certain frequency regions.

Boosting the bass with 6 dB means that the volume will increase although you didn't touch the volume slider. Assume that you have decided to use an almost perfect a slap bass sound, but you want to adjust it. Then you might notice that you get almost the same effect by turning the filter's knob as you would by turning the mixing desk's volume slider. That's because the slap bass sound contains bass frequencies only (well, almost). So if you're using filters to the change the color of the sound you might boost or cut a lot of the volume on that track just by turning a filter knob.

The two knobs for the middle region allows you to choose the frequency (knob 1) and how much that frequency region should be boosted or cut (knob 2). It's the same here with these knobs and with the treble knob as with the bass knob. If you're using an instrument on that track which has its frequency content concentrated to the mid region, then boosting and cutting the mid region will have almost the same effect as moving the volume slider on that track, so be careful.

A common mistake is to boost only. That is to tweak the amount knob to the right all the time. But filters are indeed used to remove frequencies as well. Sometimes if you feel that you need to filter a sound, it can be useful to try cutting a couple of dB somewhere, rather than boosting. The snare drum is such an example. Often it takes far too much space in the mix, because it contains a lot of high frequency content, in its unfiltered state. Cutting the high frequency content of the snare drum can make it "sit better" in the mix, blending in with, say, the vocals or other instruments. It becomes more subtle.

So when should you boost the filter and when should you cut frequencies? Well, there are a couple of easy answers. Microphone hum should of course be cut away using the bass filter. Some mixers even has a low frequency filter, which is a button rather than a knob. It cuts say 12 or 24 dB between 0 and 50Hz, to get rid of hum.

But there are other situations when it's more difficult to judge whether you should boost an instrument in the high region or cut another. One rule of thumb though is to balance the filtering almost the same way as you balance the panning. You cannot just boost all the tracks in the high frequency regions. It's pointless. It's the differences which create the result. The problem is often that two tracks are too similar and something needs to be done about it. Thus boosting both of them won't make much of a difference, but cutting one of the tracks with say 3 dB and boosting the other in another frequency region with, say, 3 dB can make a difference.

Boosting from 2000 Hz and upwards or cutting the lower frequencies of the sound, starting at 2000 Hz is practically the same. The frequency responses are similar. The only difference is that the boost resulted in a higher overall volume.

Attenuating a region of sound and raising the volume will have the same effect as boosting the region of the sound which wan't attenuated.

Almost all mixers have different filters and consequently they all sound different (mixers from the same manufacturer often have the same type of filters though). There are a few things which determine how the filters sound and how good they are. One of the most important characteristics of a filter is how steep the slope is, or in other words how many degrees the filter has.

Some manufacturers say their filters are 4th order low-pass filters or 2nd order high-pass filters. 4th order or 2nd order means that the filter cuts 24 dB per octave or 12 dB per octave. So how did we get 24 and 12? 4th order means 6 dB times 4 equals 24. Each "order" means 6 dB.

Thus each order of a filter means cutting (or boosting) the volume in half (or boosting twice). In other words, the order of a filter is measured in terms of how much it cuts (or boosts) if you move an octave up or down in the frequency spectrum. Confused?

A low-pass filter cuts off more and more of the high frequencies as you move the knob anticlockwise (down in frequencies). So if you turn a low-pass filter knob and set it to, say, 2000 Hz, then the audio below 2000 Hz will be preserved. However, frequencies at 1000 Hz will still be heard. They won't be silent. But they will be reduced with 12 dB. Why 12 dB? Because we use a 2nd order filter (2*6 = 12 dB) and one octave below 2000 Hz would be 1000 Hz. And since the filter damps 12 dB per octave then frequencies at 1000 Hz will have the volume reduced with 75% (12 dB). So how did we get 75%? 6 dB is half. Yet another 6 dB (making 12 dB) cuts in half again and half of a half is a quarter (25%). Thus, only 25% of the original sound remains and it will be damped with 75% at 1000 Hz.

But let's say you used a mixer which has a 4th order low-pass filter and you filtered it the same way as above, at 2000 Hz. Then the slope of the curve would look "more vertical" because it would cut more efficiently.

A 4th order low-pass filter looks almost the same as a 2nd order one, but not exactly the same. The slope cuts even when you move to the left (down in frequencies).

So if you tweak the 4th order low-pass filter knob and set it to 2000 Hz, as with the 2nd order filter, then it'll cut more of the frequencies below 2000 Hz than the 2nd order filter did. Frequencies around 1000 Hz will still be heard, but as you can see they are almost silent as compared to the 2nd order filter where they were only reduced by 75%.

In the 4th order case they will be reduced with 24 dB, because we use a 4th order filter (4*6 = 24 dB) and one octave below 2000 Hz would be 1000 Hz. And since the filter damps 24 dB per octave then frequencies at 1000 Hz will have the volume reduced with 93.75% (24 dB).

So how did we get 93.75%? 6 dB is half (50%). 6 dB again (total 12 dB) means 25%. Another 6 dB (total 18 dB) means 12.5%. And finally the last 6 dB (total 24 dB) means 6.25%. Thus, only 6.25% of the original sound remains and it will be damped with 100 - 6.25 = 93.75% at 1000 Hz.

With a 4th order low-pass filter which cuts at 2000 Hz you will still be able to hear audio which is located around 2500 Hz. It'll be damped, but it might still be possible to hear it. On the other hand, with a 4th order low-pass filter you'll hear less of the audio at 2500 Hz.

That's why it might be more difficult to create a good mix with certain filters. In general I'd suggest that you use at least 3rd order (18 dB / octave) filters when you're mixing. If your mixing desk features only first or second order filters, then you might consider using external filter modules or plug-ins as inserts.

But there are a number of different filter types as well and not only the order decides whether it'll be useful or not. Let's have a look at some filter types, which can be used to solve mixing problems, rather than to change the sound itself.

There are a number of filters on the market and they complement the traditional, low-pass, band-pass and high-pass filters which most mixers are usually equipped with. You might consider using them as inserts to solve problems on certain tracks.

The notch filter removes a certain frequency range (thus it creates a dip in the frequency spectrum).

It's the opposite of the band-pass filter, which passes through a certain frequency band.

So what can it be used for? Well if you don't own a dedicated de-esser, then you may use a notch filter to remove regions in a vocal recording which cause problems. And you may reduce or remove 50 Hz hum caused by bad cables or just get rid of frequencies which you don't like and which don't seem to work in your mix. Bass, mid and treble filters let you attenuate certain bands, but their frequency range might be too big sometimes, when all you want to do is to reduce a small region, such as 40-80 Hz. Then a notch filter might be useful.

A comb filter creates a metallic sound. It's frequency response is quite interesting. Different implementations have different frequency responses, but in general it looks like a comb (or saw teeth) with dips and peaks. That's why it's called a comb filter.

As you might understand, It's not the kind of filter which you use in every mix and on lots of tracks, because it changes the sound quite a lot.

However, if you're working with a sound which is dull and needs processing to become more exciting then it can be worth a try to process it using a comb filter, possibly in combination with an effect, such as a chorus or a flanger.

One of the better ways to make a sound more living and interesting is to process it through a formant (or vowel) filter. Formats are regions in the frequency spectrum which are associated with different vowels.

For example, the vowels a, e, i, o and u have a set (around 5 or 6) of peaks and cuts in the frequency spectrum and they look different for each vowel. A formant filter lets you apply these boosts and cuts in the formant regions on your track.

A formant filter can make a dramatic change to the sound, a much more dramatic change than using a simple low-pass or high-pass filter. The formant filter makes the audio sound more like the vowel which the formant filter emulates.

There are filters which adapt their frequency response to a track and make it possible for you process your track(s) using these settings. You could feed your favourite music through the filter. It checks the frequency response of the recording and then you may apply that frequency response on your own recording. E.g. you can make sure that your track has almost the same general frequency response as some of your favourite commercial tracks. How does it work? Well, assume that you know a recording which sounds excellent. And you feed it through the filter. The filter then analyses the recording and adapts its frequency response.

The filter allows you to apply or impose the frequency response of the analysed track on your own recording.

The filter adjusts the overall frequency response so the higher region of your own recording sounds more like the higher region on the original recording etc.

These type of filters can can actually transform your recording from something which sounded like a relatively dull mix to a recording which has commercial qualities.

There are two types of schools when it comes to mixing. Either filters are used to make very subtle changes to the sound, for example by cutting or boosting with 1-2 dB in a region. The other school makes use of extreme filter settings. Filters are applied to a high degree on each track, to make them sound as different as possible, making it easier for you to blend them together in the final mix.

Whichever method you choose is up to you. It also depends on which type of music you make. If you're into synths, mostly, then the synth sounds themselves have been filtered to a high degree before they reached the mixing desk. Alternatively, the filters in the mixer become part of the actual sound generation rather than being tools to put the mix together.

Filters can be used to make tracks work together in a mix. If two sounds are very similar and they are competing for the same space in the frequency spectrum, then it can be a good idea to apply some filtering on one of the sounds, or both.

Try boosting or damping a region like crazy on one of the two tracks, and try boosting or damping another region on the other track. Then their frequency spectrum's will be much more different then they used to be and the similarities will be reduced.

Arthur Andersson works at MHC Synthesizers and Effects http://www.mhc.se where he does graphical design and writes the newsletter. He's also involved with sound design and runs his own music label.