Backing track sfk files

Gordon, a customer from Spain recently asked me a question about ID3 tags on his backing tracks.

He also noticed that all his mp3 backing tracks have a strange .sfk file attached to each one and wants to know what this .sfk file is….

Hello Kenny,
I forgot to mention, some of my mp3’s have an sfk file
attached to them! What is a sfk file?

Hi Gordon

Files with a .sfk extension are usually associated with, but not necessarily restricted to, the Soundforge range of software audio programs (but could be any program that uses their audio processing “engine”).

A .sfk file is basically a little “extra” file that often accompanies the main audio file and contains information that helps your computer draw a representation of the waveform of the audio when it’s opened up in a waveform editor (like Sonys Soundforge, Acid Pro etc).

Most times it’s safe to just delete the .sfk file but sometimes it is needed for the information it contains.

A simple way to find out if it’s “surplus to requirements” regarding your system and is to do a small test. Delete one of the .sfk files and then play the corresponding audio file. If it plays ok and your audio player can still read all your ID3 information and any other file information you usually see without any problems, then you’ll know it wasn’t needed.

Mind you, .sfk files are usually VERY small files (because they only contain information, no actual sound data) so they don’t take up much room at all. For that reason, if they don’t bother you then you could leave them as they are…



Backing track audio editing

A lady from Canada, Colleen, asked me a question about audio editing:

Hi Kenny!
I have a question for you.  Can you recommend a
fairly easy program that will take my tracks and make
them all nice and even? You know how it is with
some backing tracks are more “pitchy and louder
sounding” than others etc…. I tried something called
the GAIN program, but I wasn’t too happy with it.
If you can advise me, I’d surely appreciate it. Maybe
you’ve got something advertised on your site, and
I missed seeing it, not sure…
Colleen 🙂

Hi Colleen

Ooooh, you’ve touched on a subject that really is a can of worms. Books the size of encyclopedias have been written about the subject of audio editing!

Firstly, let me say that there are lot of inexpensive (even free) software programs around the internet that will let you edit audio “easily”. But sadly you tend to get what you pay for so the easy and cheap programs usually just can’t cut it.

You say that you’re looking for an “easy to use” program, and while that’s perfectly understandable, the problem is that “easy” programs usually give poor results.

This is because audio editing is such a very complex process.

So when a software manufacturer designs a program to be “easy to use”, they have to make it do a whole bunch of things all at the same time. Audio editing generally doesn’t play too well with the “one button does everything” types of software. This is because every audio file is completely different (in fact every second of every audio file is completely different) so a software that’s easily set up and configured means it has to treat many parts of your audio with the same set of parameters.

Audio just isn’t like that. For example, you may find that the audio file you’re trying to fix has an intro which is a bit noisy or hissy, verse 1 is too quiet, the chorus is too trebly and the middle of the song is too woolly etc etc. All these problems need to be addressed individually so there is no “magic” button that can cure all (despite what some software manufacturers claim).

Audio editing is complex so, by default, the software that does this job tends to be complex also. So, any “easy to use” program you find will have had to make a trade-off in the quality of the results it achieves. This is what you probably discovered when using GAIN.

Fortunately if you buy a professional backing track from us or any of the other reputable backing track companies out there, the backing tracks will already be well balanced so there should be no need for any editing to be done to them. But I do appreciate and realise that most singers have a large collection of backing tracks that they’ve “built up” over many years which were aquired from many different sources. Add to this the fact that very often these tracks have been copied a few times between different formats (CD / minidisc / mp3 / dat / cassette etc), this creates it’s own set of sound quality issues too e.g. different eq on each track, volume fluctuations, left & right stereo balance issues etc).

The bad news is that to “fix” poor sounding audio files properly really needs good quality audio editing software…which is expensive.

I personally recommend Wavelab by Stenberg which you’ll find at:

But before you go and throw a ton of money at Wavelab, there is a free option available to you. Obviously it isn’t anywhere near as comprehensive as Wavelab, but it IS an excellent audio editor even though it’s free:

Also here’s a link to an article I wrote some time ago about editing backing tracks which you may also find useful:



ID3 tags in mp3 backing tracks

Here’s a question I received from one of our customers from Spain. It’s all about ID3 tags and why sometimes they display correctly and other times they don’t:

Hi Kenny,
A while ago i purchased an American Audio SDJ1 Player. The
player is fantastic but the problem i have is the mp3 tracks have
been transfered to the SD Card, when the card is inserted in
the machine the name of the track is displayed on the screen
but on some tracks the name dissappears after being read and
then ” No ID3 TAG” flashes instead. This doesn’t happen to all
the tracks, so how do i get an ID3 Tag on some but not others?

Hi Gordon

Without sitting in front of your equipment it’s hard to troubleshoot why it’s reading some ID tags but not others. 

However, it does sound like it may be reading ID3 version 1 tags but not ID3 version 2 tags (or vice-versa).

Most mp3 player software programs allow you to alter the ID3 tags of each song, so load in the songs which aren’t displaying the proper ID3 tag info and change the tag info. 

If your particular mp3 player software doesn’t allow you to alter ID3 tags, then open each of your mp3 backing tracks in Winamp (free download at and go to “view file info”. You can then enter all the ID3 tag information for each song. 

A nice little touch with the Winamp ID3 function is that you only have to enter the data once for each song – when you enter your song info into the ID3v1 fields you can then tell it to “copy” this info to the ID3v2 tag. Now your ID3 tags can be recognized by any program, no matter whether it only reads ID3v1 or only reads ID3v2.

Hope this helps!



Bose L1 in 300 – 400 seat venues

Gary from the UK asked a question about using the Bose L1 with backing tracks in larger venues:

Hi Kenny
I’ve just been reading you article about the Bose L1 system, I recently aquired one of these sysems and like yourself I am very impressed, my old system was a Fohhn with 1x Bass bin and 2 x tops due to the portability of the bose and the quality I am thinking of getting a second system to use alongside my existing one just in case I should get any larger rooms.

Please could you advise firstly if you recommend that if i was going to do a venue of say 3-400 that “double” system would be suitable?

Also which is best way to link 2 x systems, do you link directly from amp 1 to amp 2 as in conventional amplifires or is it best to get a “splitter” from the one output on the tonematch and go indipendantly into each system?

Also am a little confused on the follow up article abot L1 and L1 classic, I thiught there were just 2 versions of the L1?

The L1 with the round base and the Mark 2 with more square base does this now mean there are actually 3 versions?

The system I have by the way is Mark 1 with 2 x bass bins and 1 x tone match which I am thinking about doubling with another Mk1 and another 2 x bins.

Any information would be much apreciated,

thank you very much,


Hi Gary

Good to hear from you.

I would say that two Bose systems would probably NOT be enough for playing to crowds of 3 – 400.

Two systems might just be enough, at a push, but it would have to be in a 3 – 400 seat “theatre type” environment – by that I mean where the audience are seated, are quiet and listening to you.

If you tried to use two L1 systems to get above the noise of an audience talking, dancing around, ordering their drinks, clinking of glasses and general burble of a crowd, then two systems would not be loud enough to cut through to 3 – 400 people.

Worse still, if you’re using two of the newer L1 500watt systems, they probably wouldn’t even be enough for a “quiet” theatre gig of 3 – 400 people.

You are correct about the different models.

There are 3 models, the 750w L1 Classic (round base), the 500w L1 Model 1 (round base) and the 500w Mark 2 (square base). The L1 Classic and L1 Model 1 look exactly the same (round base) which is what causes confusion.

Bose don’t sell the round base L1 Classic any more (the 750w model) so anyone who’s bought an L1 round base version in the last 6 months to a year most probably has the newer 500w model. You mentioned that you have the Mark 1 but don’t say if it’s the L1 Classic or the L1 Model 1 so depending on which vesion you have, it will be either the 750w round base model or the 500w round base model.

If you have the 750w L1 Classic you may struggle to find another 750w system because Bose don’t make them any more so you may have to settle for the newer 500w version which isn’t as loud.

If it’s any help, if I was booked to play a 3 – 400 seat cabaret/club type gig I would want to use my two L1 750w systems with two subs on each PLUS a couple of conventional 15″ or 18″ bass bins and amp. The Bose systems would handle just enough mid’s and hi’s to fill the room and the conventional bass bins would give the extra oomph needed for the bottom end required in a venue that size. I may alternatively consider using another two subs per side instead of the conventional bass bins (ie I would have 1 Bose pole and 4 subs per side) which would give me 2000w in total, probably JUST enough for a 3 – 400 venue. I’d keep my fingers crossed the audience were not going to be too loud or rowdy! Ideally, 4 Bose systems would suit a venue like this – I’d have no reservations about playing a 3 – 400 seat venue with 4 “poles” with two subs on each.

As regards connecting up two systems, I prefer to run my two L1’s in stereo. I find that they give a much better sound when used in stereo.

Conventional PA systems are (in my opinion) better run in mono because the audience members seated on the left hand side of the room can’t hear the music coming out of the right hand speakers (and vice versa). So stereo sound is all but lost when using a conventional PA in a cabaret room type environment.

However the Bose L1 disperses the sound around so incredibly well, that you CAN run two of them in stereo and everyone, no matter where they are seated in the room, will hear everything. Stereo works really well when using two Bose L1’s and sounds fabulous.

Hope this helps!



How to save money Christmas 2008

The credit crunch is affecting everyone, make no mistake about that.

Even those who are fortunate enough to still have a great paying job and plenty of gigs are still looking at that nice bundle of money in their pocket and thinking “I better not spend it all…who knows what’s gonna happen next year…what if I lose my job, what if the gigs dry up…”.

So there’s never been a better or more important time to be a little bit prudent with your finances than now, Christmas 2008.

And I’ve got a great little tool that could save you a fortune this Christmas.

You’ve heard of eBay right?

Well, eBay isn’t just about individuals selling their old junk. Many of the biggest companies in the world operate on eBay. And like all big companies…they often make mistakes.

And I’ve got this great program that easily sniffs out items for sale on eBay that have been MISSPELLED.

Why are misspelled eBay listings important I hear you ask?

Well, if an item on eBay has been listed with a spelling mistake, it won’t show up in the normal eBay search results.

This means less people know the item is for sale, which means there are less bids on it.

This lets YOU nip in there and grab it at a bargain price.

I’ve been using this tool for quite a while now to GREAT effect.

And because it’s Christmas (and you’re taking the time to read my blog) I’m letting you in on the secret too.

Go try it out, it’ll cost you nothing and it may just save you a small fortune:

Merry Christmas!


Backing Tracks On A Laptop

Thankyou to Neil from England for submitting this question: 

A question for Kenny. If I used a laptop to play my
backing tracks on stage, would I need a good sound
card in the laptop or would the sound be fine when
amped through the PA?

Hi Neil

Generally the quality of sound you get from your laptop WILL be dependant on how good the sound card in your laptop is.

However, most computers (and even cheaper laptops) manage to put out a reasonable sound quality and if you’re playing your backing tracks in a live environment where the audience are talking etc, usually the general burble of noise in the venue makes any small sound quality issues pretty much unnoticable.

I used various laptops on stage to play backing tracks for years without too many problems (before moving on to using the iPod).

The only downsides to using a laptop on stage are the obvious ones – keeping it away from spilled drinks, making sure no-one trips over the power and audio cables and bring it crashing down on a hard stage floor, the abuse the keyboard can sometimes suffer when being used in the high charged excitement of a gig, and the audio output jack (and mains plug) tending to break because they’re being continually plugged and unplugged at every gig (they’re only plastic and eventually just break).

Also bear in mind that there is one other well known issue with laptops when using them for playing music live on stage – and that’s mains hum.

It’s very common (and very annoying) and is caused by an earth loop. Sometimes it takes the form of a loud hum but in some laptops it sounds like a low frequency crackle, a bit like if your TV wasn’t tuned to a channel properly. There was a school of thought which suggested that the chipset on the laptop motherboard could be to blame for this because the interference seems worse on some laptops than others, but as far as I know nothing has ever been proved one way or the other. The interference is most noticable when the music is either not playing at all or during quiet parts of a song.

Whatever you do DO NOT do what a friend of mine did and remove the earth wire from the laptops mains plug!!! Earth loop noise can be safely, easily, and inexpensively cured by buying a simple ground loop isolator which only costs about £12 (go to and type in ground loop isolator in to the product search box at the top of the page)…