Submitted by anonymous on Mon, 09/22/2003 - 11:11

I have been reading up quite a lot about recording and mixing. Why do you have to mic the guitar or bass amp? Why cant you just feed it directly into the mixer?

Thanks :)

Comments

Audio Gaff and Uncle Bob both make very good points. The truth is you should record direct at times and with an amp at others. It all depends on what type of sound you're looking for. If you want a very clean sound, direct would be the way. Running the guitar through an amp and speaker is essentially a distortion generator and a low pass filter. Even with clean settings on the amp, a speaker and amp will add a bit of "edge" and roll the highs off above 6 or 7 kHz. You are also introducing the effects or "sonic signatures" of the mic and the mic pre into play.

The best thing to do with any recording technique is to try it. It won't hurt anything unless you try to plug a speaker level signal into a line level input! :D Kurt

From my limited experience and habit of tending to overanalyze things till they don't make sense:
The wonderful world of electronics comes into play. Direct sounds artificial - totally dry signal without any reverbations, and broadband response - two of the factors which directly detract from how "natural" something sounds.

Putting it through a cab, then micing the cab will:
1) Pick up room sound - even at levels much lower compared to the signal, that reverbation adds to the naturalness of the sound - the ear isn't used to hearing things without any reverb whatsoever, which is why direct sounds... sterile. Ever stood in an anaechoic chamber?

2) Pick up certain frequency ranges better - Direct signals, especially distortion/OD guitars, tend to turn into broadband white-noise. Any natural acoustic instrument will have it's frequency range where it is the most active. Using a cabinet and mic will accentuate some frequencies more than others, and make it sound more like a real instrument again, rather than a mess of white noise. Ethan always says that an different frequencies propagate away from an instrument in different directions, and this makes a lot of sense to me personally. In my experience, this is very true of cabinets - placing a mic on-axis and off-axis gives very different sounds. Also, like Kurt said, most heavy-duty cabinets tend to filter out everything over 7kHz, which is where a lot of the jarring sound from direct guitars come from.

Boosting certain frequencies will sound more like an instrument again - basically what micing a cab does.

Tangent: I own a PODxt and I use its amp simulation along with a flat-response keyboard amp. Great sounds coming out of that for playing. So far though, I've been recording direct from it with some fantastic results. (In my ears, though. Kurt will probably strangle me again :D )

I probably should experiment with recording two channels - one by micing the amp, one going direct from the POD, then mixing them together.

If one is miking a bass cab, they must intentionally desire the (limited) tone available from most commercial bass cabs. Note this is separate and distinct from recording tube amp grind, which requires miking a cab.

A 4-string electric bass produces a fundamental of 41 Hz, and a highest usable harmonic between 5,500 and 7,500 Hz. At the tuning frequency, vented cabs produce all the output from the vent, and nothing from the cone. Cone output increases and vent output decreases as the frequency moves away from the tuning point. Close miking the cone loses the output from the vent.

There are no bass drivers that span the entire frequency range, so another driver is required. Usually this is a crappy piezo tweeter with wildly varying response patterns and a harsh response. Close miking the bass driver also misses the output from the tweeter, so the mic must be placed far enough away to capture the vent, bass driver and tweeter.

Last, nearly all commercial cabs are built to produced a big hump in the mid-bass, 80 ~ 125 Hz. This produces "saleability" from the illusion of big bass, when it is actually a boom produced by stuffing the driver into a too-small cabinet. It cuts through well in a live venue, but rolls off drastically in the low end. Listen to one of these cabs with full range music from a CD, then determine if you want your bass to sound like screaming through a wet blanket.

A quality DI such as the Countryman 85 for passive basses, or Raven Labs for active basses will deliver the full range of your bass to the board. And yes, DI is completely dry.

Not all bass cabinets are vented...I can only assume by your response that you are referring to the 'New' modern cabinet designs which because of their inner dimensions require vents and ports in order to reproduce the frequencies you alluded to.I do accept the fact that some of the 'cheaper' companies bild in false bass frequency response in order to boost sales.I take exception to this thought that ALL companys are doing this.There are some wonderful marvels of quality engineering available these days that allow the bassist some latitude on cabinet size and weight.I'm old enough to remember the days of my full on Ampeg SVT rig and a couple of other cabinets at the same time.Or my old 360 Acoustic rig...Thank gawd theres some smaller yet quite usable and responsive options today.I just dont have the energy to lug the big stuff around, though I do still possess and use a Cerwin-Vega B36mf when I need some real LOWS.

BTW...I always took a mic feed from the SVT cab(usually a LD condenser) and a DI and mixed them liberally for studio work.ymmv

I have extensive knowledge and experience in subwoofer engineering and bass cabs, spanning more than 30 years. I'm old enough to remember how excited I was when Thiele and Small published their works and took the mystery out of vented design.

The inner dimensions of a cabinet have absolutely no bearing on whether or not a vent is required. The driver characteristics, specifically the EBP, dictate the use of a sealed or vented cabinet. Vent parameters are entirely a function of tuning frequency and air velocity in the port.

Sealed cabinets have less low frequency extension and are less efficient than vented boxes. However, they also offer much tighter bass response than vented boxes due to significantly lower group delays. Because of this, sealed boxes are the audiophile's choice for bass. At a modest volume level, or a home setting where room gain increases bass response, a sealed box can be EQ'd closer to flat response. The Bag End ELF system is a sterling example of this technique.

Sealed performance cabinets such as the Ampeg produce very little fundamental below 60 Hz and therefore do not reproduce the signal as created by the bass guitar. They are designed to be seriously loud, and the design compromise is reduced low frequency response. The Ampeg offers a very specific tone, which is altogether different from accuracy. Tone is subjective, accuracy is not.

Sealed boxes offer a number of varying Qtc values that are achieved by varying the box volume for a given driver. The higher Qtc values are more boomy, and the lower ones are tighter. Cabinet volume increases with the lower Qtc values. None can match the lower frequency extension of a vented cabinet at the same level of efficiency.

It is not just the "cheap" companies that build mid-bass boom into their cabs, but many of them. SWR, Ampeg, Crate, Carvin, Fender, GK, the list goes on. The reason is perceived loudness. A full range bass cabinet is less efficient, due to the laws of physics. It is hard to compete in the market when your cab is 10 SPL less sensitive than your competitors' product. The Acme is one notable exception. The Acme has a small but dedicated following of bassists who prefer the full bottom provided by an audiophile cabinet. I've not had the pleasure of testing an Accugroove, Bergantino, or Aguilar yet.

The Eden XLT series has a massive hump (the Eden honk) in the mid-bass range, and it is a premium priced product. The Eden drivers (4x10) are stuffed into a far too small cabinet, resulting in the midbass hump, and corresponding steep rolloff curve. I recently had a D410XLT on the test bench, and it is a gutless wonder below 50 Hz.

Vented boxes are neither new nor modern by any stretch of the imagination. Sealed cabinets are much easier to build, and vastly more forgiving of incorrect driver/cabinet matching than are vented boxes. Sealed boxes are cheaper to manufacture.

The design triangle is Small-Efficient-Low. You can have any 2 out of 3, but not all 3 in the same cabinet. A small, low cabinet is not very efficient. A efficient (loud), low cabinet cannot be small. The solution is packing several kilowatts to drive inefficient subwoofers.

As a working bassist, I cart around two 1x15 subs, two 1x10 highs, and an 85 pound rack full of biamp gear, sub-synth, EQ, and 3,000 watts to drive it. Hand-truck loading this gear, week in and week out, does get very old.

Back to recording, tone is subjective. Musicians wanting to record the lowest fundamentals produced by their bass, will have to use a DI (or ELF) somewhere in the process. Tracking is not my area of expertise, but I think a mic + DI on separate tracks would provide the most control during mixdown.

I have a vast amount of reference data on my web site, free for the downloading.

http://www.ofgb.org/reference

My "Musician's Reference" spread sheet is a work in-progress and has 1,147 drivers cataloged as of this writing. Each has the cabinet specs listed for the various alignments, and many have the SPL numbers plugged in.

I know how to produce bass, but do not (yet) know how to record. That is why I'm here... :D

I have checked yer site ...BG and its got a lot of great info....nice job......as far as recording bass...and this is something I do quite well, you cannot go wrong EVER with anything that has a Jensen transformer connected to it.The countryman has been and still is a go to device for this.Recently I've experienced the beauty of the Avalon U5 DI....amazing....I'm sure theres others but these are so damn simple and require only a cable or two to do the job. I did track some bass recently through a True Systems P2 analog preamp.It was quite splendid as anything associated with Neumann should be.

The blend one can achieve through the use of something of extreme accuracy ala DI and the micing of a cabinet in my opinion,is the way to achieve the best of both worlds.I have gotten killer sounds with an SVT cabinet miced @3-4 feet out witha U87 Neumann and another line taken from a Countryman passive DI....of course this was with my old 62 P-bass...which sounded like BASS through anything.

I sometime use the countryman with a Neve 1272/1073 but more often I use an Evil Twin (goes down to 8Hz) and a mult to an API 512C with each going to either an API 525, LA2A, Tube Tech or Vari-Mu. Then mic the cabinet and use what's left over for that. At mixdown I may only need one path and other times I may use all three and may even insert another flavor on one of those.

I make an arrangement of:
(1) a klark teknik DI for direct injection
(2) a Beta 57 capturing bass cabinet
(3) GT55 also capturing bass cabinet
(4) a direct feed from the bass amp pre

Each signal goes to its own track and of course, we genereally do not use all the options above, (watching for phase) but clients get very happy having few different tones to chosse and/or blend.
I would say that in 80% of times, clients as well as me prefer (1) and (4).

Usually I prefer recording guitar or bass amps through a mic. I like the natural sound. Allthough you might get a little more punch when you line the amp instead of micing it, and of course you would need to crank the amp up a good bit if you want any headroom in your sound, this is espessially important if you are using a Fender tubeamp and are going for that crispy/clean sound that fender amps are soo famous for.
A good compromise in the case when you dont have access to a soundproof studio where you could really crank your amp, might be a digitalpreamp like line6 pod or digitech genesis 3. Or if you are more into analog sounds you might go for HK Tubeman or Red box pro.