Audio Guide

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Introduction

On behalf of Jimzinsocal, IAmGhostDog and myself, WELCOME to the Audio Corner.

Audio is probably one of the few things in computing where numbers aren't really an issue. There are few 'Gold standard' tests for objectivity so whatever info you get in this forum is mainly subjective and dependent on what we have experienced through our ears.

That entitles you to disagree but not flame.
That also entitles you to tell us everything about something that you have so others may be informed about that product.

So relax, sit back.. and enjoy the music.

Cheers.


all others with contributions, please post in this thread. Here (aka Audio FAQ)


Credit:
Massive Thanks to Amol, Mjollnir, Sangram, Doctor Cilantro, and my partners in crime; IAmGhostDog & Jimzinsocal.


Great Ideas for Audio Corner:
1) DAW (Digital Audio Workstation) thread.
2) Vinyl Links
3) What's spinning on your turntable tonite?

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Hearing.

Our ears are transducers. They convert sound waves to kinetic energy and then to chemical/electrical energy. When sound is created, it produces vibrations which vibrate the air molecules which then vibrate other air molecules and so on until it gets to our eardrum which vibrates and signals the brain that there is sound. This is extremely simplified and is done a lot better by HowStuffworks.


Decibels? SPL?
Decibels are loudness units. Kinda like mph/kmph. Unlike mph or kmph however, decibels do not scale linearly but logarithmically.
SPL = Sound pressure level.

A doubling of volume is approximately 10db.
so a 100db is twice as loud as 90db
and FOUR times as loud as 80db
and EIGHT times as loud as 70db
and SIXTEEN times as loud as 60db
and THIRTY TWO times as loud as 50db.

The other interesting thing to note is that to reach such volumes also requires exponential increases in power.
you need TWICE the power to increase volume by 3db.
so to double the volume, you need approximately 2x2x2 and a little bit. ie; we'll round it up to 10x the power required to double the volume.
Confused?

Read here. This site seems to be my saviour when words fail me.

Two sources of 20 dB output each will not add up to 40 dB.

20 dB + 20 dB = 23 dB.

When the sound pressure is doubled, 10 decibels (or 1 bel) have been added. That is, a little more than three times the *power* has been applied (3+3+3+1/3) to increase the sound pressure by 10dB. The scale is logarithmic.

To double the sound pressure level of a system, we need a lot of power. If the output has to be increased from 80 dB to 160 dB, we need to increase the power by a factor of 75 times, or from 100 watts (say) to 7,500 watts!!

Waveforms
Read this first.
Essentially, nothing is lost. Digital 'waveforms' are actually steps and therfore are more prone to sampling errors and 'lost' information. CD's have tried to be good but compared to vinyl, they can sound 'thin'. This can somewhat be offset by an excellent mastering process or a very good mixer. However on decent high end speakers, you can hear and audible difference. IF you can't... BE GLAD. That means your ears cannot appreciate the difference so you dont' have to spend money upgrading speakers all the time.

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Basics of Music

can anyone chip in here?
thanks.

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Codecs

Digital Audio Primer - Thanks Jimzinsocal.


This was originally posted by Amol
Excellent job

Amol Says:
There are certain lossless encoders avaiable.
They are
Monkey's Audio
FLAC encoder
Optimfrog
WMP 9 lossless
being the most popular.

There are certain Issues with FLAC that it does NOT produce perfect lossless files. Although it might not be true, but certain people have been showing difference in the quality of the original wave files and the encoded FLAC files by hearing tests.

WMP 9 - Can only be played in windows media player 9 and not compatible with other players AFAIK

Monkey's Audio codec is the best out there as far as compatibility and compression quality and speed is concerned, although it isnt as fast as some other lossless encoders , it makes very high compression files around 60% of the original size.


here's the download link..

Optimfrog is not very popular yet,and no MPEG taggers support it.




CONVINIENT TO USE MPEG TAGGERS..

MPEG audio collection- The ultimate all in one easy to use tagger for all mpeg files like .vqf, wma, mp3, ape etc..
Get it
Here

Another good mpeg tagger is mp3tagger
Download it
Here..


CHECKING THE QUALITY OF MP3s

ENCSPOT version 2.0 basic
Here's a superb tool that can accurately determine the encoder used and the accurate number of frames in the mp3, the vbr scale used, the type of compression, etc, and also determine the quality of the mp3s.
get it Here..

I hope someone finds this useful

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Amol again

The argument about the best MP3 encoder still goes on..

Some argue that LAME encoder is the best, but contradictory to it, the latest FHG encoder (version 4.2) perfoms the best in terms of audio quality, and provides a certain sweetness to the music compared to LAME that sounds a bit harsher than FHG. The only gripe is that the normal consumer level FHG encoders like music match jukebox or Itunes dont let you tweak your encoding beyond a certain extent.
Because Itune doesnt let you select the cutoff frequency for mp3s, ( the default cutoff frequency is 16 Khz for FHG), and musicmatch doesnt allow you to encode VBR at the highest quality setting.Instead it uses the fastest setting for encoding and doesnt let you use the encoder to the maximum extent. For making the full use of the FHG encoder following are the softwares that let you tweak your encoding to the maximum extent.

Cooledit Pro 2.1 ( now adobe audition)
Steinberg Wavelab 4
MAGIX mp3 maker diamond 2004 ( the best )

Although these softwares cost money , they still let you use the best encoder out there.

For LAME, use the version 3.90.3 that is acknowledged to be the best known for quality.
you can get it here...

For the front end tool for Lame that is a proper GUI get RazorLAME here..

Encoding at low bitrates 128 kbps and 160 kbps sound the best with FHG hands down. After 192 kbps the difference between LAME and FHG tightens.
[/end Amol]


Also, check out the guide below and 2 programs which are EASY and simple to use.

How To Rip the Perfect MP3 Collection - TitanMan
Cdex - simple ripper and encoder
Freerip - simple ripper and encoder - Free!!

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Media Players
Media Players - any takers to update this with Foobar and winamp 5?

Winamp 5 is basically winamp 2+ winamp3 = Winamp 5 Get it? Easy to use with plenty of plugins and skins. Free and IMHO, hassle free.

Foobar is also free, but has a slightly unfriendly interface and is very plain. The decoder is reputed to be one of the most accurate. So check it out.

Soundcards
Basically there are 2 kinds of soundcards.

Onboard and standalone.

Onboard comprises of :
C-media, Realtek and Soundstorm (digital output only) - Alternate Remix Drivers

Standalone can be further divided into consumer or pro cards.

Consumer level
1) M-audio Revo 7.1
2) Audigy 2 - Alternate KX drivers
3) TBSC. - a little long in the tooth. But great for just plain music.
4) Chaintech AV-710 $25 - has optical out.

Professional Level
1) M-audio 24/96
2) Terratec DMX 6fire
etc.

In Short:
Audigy2 - most feature packed;

• Dolby Digital-EX Decoding
• DTS-ES decoding
• DVD-Audio
• EAX 3/4
• etc

M-audio Revolution 7.1 - Excellent for music with playback matching a dedicated CD player; check reviews above.

Edit: Re: Doom 3

Is it true that Doom 3's audio engine is entirely CPU-dependant, thus negating the benefits of high-end sound cards? If so, what are the benefits? What are the drawbacks?

Yes, we do all sound-mixing in the Doom 3 engine and don't rely on high-end audio hardware to help out with this aspect. Moving it over to the audio card would have a negligible benefit, as our current sound-mixing takes up only a few percent of the CPU.
The benefit is that we run the same code-path on all systems. The only drawback is that we run the sound engine in a separate thread, and keeping up with the sound synchronization issues has at times been a bit of a headache

Much to Creative Labs chagrin, Doom 3 should sound exactly the same (and perform equally well) on your motherboards built-in audio processor as it will on a high-end Audigy 2 ZS sound card

Here

UPDATE: Creative and ID patch up



ASIO- Here is a definition of ASIO
ASIO

ASIO is more useful in recording rather than playback for ultra low latency recording sessions, which would result in stutter free music recording. It is designed to bypass any software restrictions or interferences put by the OS , and communicate directly to the sound card's controller to reduce latencies.

For music playback it can also be beneficial, as it would bypass any sampling done by the OS itself, and result in a sound that is the soundcard meant to give.
Hope this clears up a bit [/Amol]

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Speakers

I'll try and make this simple.
Speakers are probably THE MOST IMPORTANT link in the chain for audio equipment. Good speakers are meant to reproduce sound as accurately as possible. good speakers should try and recreate an atmosphere of 'realness' and authenticity.

I will not go into the details of how speakers work (Howstuffworks) but rather what kinds of speakers are available out there.

• Diaphragms - most common
• Planar - Magnetic - Magneplanars
• Electrostatics - Martin Logan
• Horns - think Klipsch and JBL

Most PC speakers are diaphragms with Klipsch and Monsoon having horns and planar speakers respectively. The difference between the types of speakers has to do with the sound. Not all speakers sound the same and that difference is usually due to

• cabinetry
• drivers
• room placement

Search the forums for even more info regarding different types of speakers or post a new thread for help.

Rule 1 - and there is only one rule
Its really hard to put down a guide to buying speakers because it basically boils down to 2 things.

• Cost
• Sound

So if it fits the bill and sounds decent to YOUR ears. Go for it. That's my advice. Simple ain't it?

Amol says:
Wattage- The basic unit for energy measurement.
Wattage in music= sound power (not loudness) and "physical" pressure
Loudness in music = defined by decibel pressure , human ear can tolerate upto 135DB loudness pressure, 135 db will actually make us deaf. 80-90 DB is the kind of loudness our ears can tolerate on a regular basis, anything beyond that and our hearing ability will start diminishing very soon.

PMPO is defined as the peak maximum power output, which is just a gimmick to earn more sales. It is defined as the end limit of the speaker's abilities , just measured for a second or so.

RMS - root mean squared output, the highest power output the speaker can give over a measurement statistically. But the speakers are usually rated on the basis of burst RMS or peak RMS , that the speakers can give. But you should always look out for sustained poweroutput. For e.g. Altec lansing 621 speakers are rated at 200 W peak RMS. But they are rated at 143 W sustained RMS.
Anything above 100 W sustained RMS should be good enough to shake your house.[/Amol]

A listing of PC speaker reviews + audio equipment
Speakers 101
How Many Watts is That Speaker?
Computer Speakers
Good PC speakers
Read pakman's thoughts.
550 speakers and Realtek combo
550 speakers and A2 combo.
Megaworks 650 and A2
Speakers that will work with Soundstorm

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5.1 speakers but no 5.1 sound (using onboard 6 channel sound)


This seems to be a common problem on the boards so I thought I'd discuss it here.
getting 5.1 speakers and the onboard 6 channel sound doesn't guarantee 5.1 surround sound.

"BUT I THOUGHT THE MOTHERBOARD SAID IT SUPPORTED 6 CHANNEL SOUND!!!!"

Hang on.. it does but you gotta have the right software to use it.

DVD's
All DVD's have PCM stereo soundtracks. Most will have Dolby Digital 5.1 and a smaller percentage will have DTS 5.1.
The soundtrack exists on the DVD in the form of a digital stream which has been encoded. To listen to it, one must decode the stream into the native 5.1 format.

How do I do that?
2 ways - Software & Hardware.

Onboard sound will do the decoding of the dolby digital 5.1 (DD5.1) with PowerDVD or WinDvd using the CPU. - This is software and is the only method for those without Audigy soundcards. BE WARNED - only the paid versions of PowerDVD or WinDVD can do this. The OEM versions that come with your DVD drive or Motherboard usually only allow 2 channel PCM stereo sound. (sucks eh?) Some nicer manufacturers actually bundle the versions that can decode DD5.1 and DTS. so check beforehand.

To do this: Enable 6 speaker in the PowerDVD/Windvd 'AUDIO' tab. check that your speakers have been selected to 6 speakers or 5.1. Done. enjoy your movie

Once decoded, there are now 6 channels of sound so your onboard soundcard can send it to your speakers. YAY!

Note: The OEM versions of software players are good enough if you have an Audigy or an external receiver. Just ensure that SPDIF pass through is enabled in the Audio tab.

but you said something about hardware

Ok. there are only 3 soundcards that can decode Dolby Digital.
1) Audigy 1
2) Audigy 2
3) Audigy 2 ZS (also does DTS)
and 4) external receiver

AND NOT SOUNDSTORM

how do i use this?
Go to powerDVD or Windvd and go to audio options and check Enable SPDIF out or Enable Digital out... or something similar.

Like so:



go to audioHQ and check AC-3 decode ... Ta da!


Also with external receivers.. check the SPDIF bypass in AudioHQ and check digital output and ensure you have either a coax digital cable and optical cable connected from soundcard to receiver.

GAMES

there shouldn't be a problem with games unless you've set it up wrongly. go to Control Panel and check to see if you've selected 5.1 speakers. Play a test tone from the driver control panel.

MUSIC
Music is primarily Stereo ie: 2 channel. getting it to play over 6 speakers is not an issue.
Using winamp:

Ctrl-P.. click output.... enable waveOut output and play a song..
you should be sweet.

using the audigy's CMSS 3D.
Go to EAX console and go to CMSS.
and play with what you like best.


Update: Hmm interesting programme Cinematic MP3
turns Mp3's into 5.1


Audigy to Receiver

Via a digital connection: you need this

Found @ Radioshack
Catalog #:274-897
digital connection will only give you STEREO in games and music.
you will need to check Digital Out and uncheck AC-3 Decode so your Receiver can decode the DVD signals.

Via analog connection: you need 3x

Found here
Catalog #:HOS CMR206
hope it helps.

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Digital Vs Analog

Having 'Digital speakers' is a misnomer. Digital speakers for PC's are unique because they function as a receiver with decoding capabilities.

Digital speakers??
Firstly, digital speakers allow a digital connection from the speakers to the soundcard/motherboard via an SPDIF header. This method of connection is better than an analog one because it allows less interference to be picked up like AC power cables, hum, static etc. The problem with a digital connection is that you can only get either a PCM Stereo signal or an encoded Dolby Digital or DTS signal, and not 5.1 from gaming or other music sources.
The other issue is that the DAC's (Digital to analog converters) are done by the speakers. It may be a good thing if your speakers have very good DAC's but can also bite you if they aren't the best. Therefore going digital is the BEST solution if you have Soundstorm.

Check these 2 threads.
nForce2 Boards WITH Soundstorm
Speakers that will match Soundstorm

[ A DAC converts a digital signal to an analog one as speakers can only use analog signals; there are exceptions but those exceptions are not in the realm of PC speakers]


Analog Speakers
Analog speakers are the MOST common forms of speakers available.
They will work with almost all PC audio solutions. The issue with analog speakers is that they do not have any processing capabilities of some of the Digital speakers. IMHO, that isn't really a step backwards as an Audigy 2 has all the decoding capabilities built in and there are software solutions to take care of the decoding capabilities.

Therefore in summary: There is NO difference between digital and analog speakers. It is more important to get a GOOD set of speakers and match them with a good soundcard than it is to go and get a digital set of speakers because they are 'digital'.

I hope this clears it up. Don't buy the marketing

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DVD & Movie Basics


Surround sound formats
DTS, Dolby Digital & DVD - A history
How to Setup a Basic HT
Speaker Placement


Bose
Before buying Bose. I suggest reading these articles first. Many people swear by Bose. I don't and I think one needs to make an informed decision before buying Bose. Remember, don't buy the marketing.
Bose
Liquidtheatre

Connecting to Receiver
Audigy - Look above to find out how to connect the Audigy soundcard to a receiver.

Analog - - as many of these as required
For 5.1 - 3x of these (1x Fronts, 1x Rears, 1x centre/sub)

Digital -
Coax -$4 for 6 ft.
Optical - -$14 for 6ft

There should NOT be any difference between types of digital cables. As long as the data gets transferred across it will be fine. It has been accepted that Coaxial cables are less prone to jitter simply because they have less conversion taking place compared to optical cables (from electrical to light and back to electrical).

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Tips + Tweaks

Audigy install guide
Vinyl to MP3

Massive thanks to IAmGhostDog for both guides!

Amol's Mod

Doctor Cilantro speaks


The common man's cry:


"I've noticed that whenever i'm playing some audio, with either one of my sound cards and i concurrently access my scsi drive i get warbling and dropouts in sync with the data transfer. Anything i can do to fix this? It only happens with my scsi drive which is on a fairly recent Adaptec ultra scsi 160 controler. I've tried messing around some with the PCI latency setting as well as swaping the scsi card to a couple of diffrent PCI slots. System specs in sig."

"I have this problem with winamp where I minimize winamp to the desktop and it starts burping and popping. I have uninstalled all kinds of software, service packs, etc. I only have this problem with winamp (dvd audio works fine and media jukebox 7 as well)...ever since I rebuilt my system with RAID 0. I know it's a long shot...but has anyone had any kind of audio troubles w/ the highpoint in effect. "

"Do you find all of this as amazing as I do, dear reader? To be clear: I'm not surprised that the PCI latency settings have such effects on the system as a whole. I have a background in engineering, so I have some knowledge of such things. There are two things, however, that I find very surprising: (1) that BIOS settings can be so freely ignored by individual devices, and (2) that manufacturers are providing such awful defaults with their hardware. I'm sure ATI has their card configure itself to a latency value of 248 so that they can avoid all kinds of technical support calls from persons whose machines can't keep up with the card at a more reasonable setting. But that utterly screws other users, and it does so in a way that isn't simple to diagnose or fix. How many users, after all, are intimately familiar with the PCI specification? How many users are computer-literate enough to go poking around in their BIOS or use PowerStrip properly? From my dealings with the larger community, I think the answer is "not many".


In retrospect, it angers me that when I've tried to work through such stuttering, hitching, and pausing problems in the past with various technical support persons, they've blamed interrupt sharing, my operating system, my drivers, the way the device is configured, my other software, and pretty much everything except their own device (and certainly not its PCI latency settings). Sure, I've had technicians tell me to try adjusting the PCI latency in the system BIOS, but that's utterly bloody useless; it doesn't matter what that's set to if the devices in your system configure themselves otherwise. The system BIOS on my wife's machine lets me tweak the PCI latency setting, but I've found exactly the same thing with her machine; i.e., it doesn't matter to what I set PCI latency in the BIOS, some of the cards in her machine configure themselves far differently anyway.

So, I've just slaughtered a host of annoying system bugs with the application of one simple utility. As you might well expect, I've already purchased my copy of PowerStrip, and that was $30 well spent. If only I had known about it sooner. If you've got any such problems with your system, I suggest you try it. It just might save you hours of time. Be sure to read all the tips and help stuff, however, for using bad PCI latency values can hang your machine pretty easily.

--------------------------------------------------------------------
When I had RAID, I had major problems, I tried upping winamp's priority, setting resources for background apps, etc. Nothing worked. Recording to the system drive (c of the RAID array was corrupted. The only fix was moving the paging file to another drive and tweaking the PCI bus 'latency' for the adapters; I lowered USB, Network Card, Video Card to around 80-90, etc. and then benched with ATTO after rebooting to find a "sweet spot"......what a pain in the a$$. The video cards are defaulted at 248ms. This wasn't really a fix either; it didn't feel right, I had to take a hit on HD performance, ...it was a pain in the ass.

I would highly recommend a re-install in Standard PC mode and disable any ACPI features (prior to install) in the bios and any other ports or devices you won't be using. You can work around a re-install (possibly) by copying your profile and configuring the new one for standard pc and then reboot into that profile but a re-install is best. If you try this there is a step by step procedure you should follow, which I can provide. AIDA32 should be used to check IRQ resources...do not trust Windoze.

Things to try:
-------------------------------------------------------------------
Disable APIC

"The reason for stuttering remaining even though you dont have IRQ sharing from what I can gather is that nvidia may have a borked implimentation of ACPI in hardware... its certainly been a problem for via, ali and sis in the past...

Also consider that ACPI is controlled in hardware by the southbridge (traditionally, so I'll assume its the case with nF2), which in the case of nForce2 means the ACPI controller has to share with NICs, a Hypertransport controller, the Soundstorm APU AND all the other legacy I/O stuffs... That southbridge is going to get mighty hot.

Some people have found that by applying a small heatsink to the southbridge then that cures their problems, some have found that by switching to the StandardPC then that cures their problems... both methods aim to take a load off the Southbridge, one in terms of heat control, the other in terms of reducing load on the Southbridge.

So long story short, I give the StandardPC HAL two thumbs up. After swapping back to the StandardPC HAL, you'll want to reinstall/enable APM to get power management features back.

The one thing to note about APIC, the extra IRQ's it gives are only virtual, from what I can gather they all map back to whatever IRQ the ACPI controller is on, usually IRQ #9."

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Use a NIC instead of onboard LAN
Disable in BIOS device/features not used
Disable smooth scrolling (in IE Internet Options>Advanced)
Move Paging File to another IDE channel (recommended anyway)
Update BIOS/change Video/Audio drivers
Use Powerstrip down adjust PCI bus allotment to devices
LINUX



Okay so I made the jump to XP. I was still sharing an IRQ between the ATI video card and the M-Audio sound card. I should have just moved the M-Audio doen a PCI slot, but I had been that route before in Win2k, and it didn't work; plus I was so frustrated my mind was jumbled. I re-installed XP in Standard PC configuration.

I have since enabled the advanced power features of XP in the Power options of the control panel. I can now shutdown, hibernate, etc as before.

After some hemming & hawing (but not much) everything is working rock solid. So to guarentee a good setup you may want to just go Standard with the install to be safe; I haven't had any problems.

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Mjollnir speaks

You might like to reconsider moving your paging fie... From this resource and others, it seems clear to me that it is a good idea to maintain a paging file on your system - best performance is suggested to be when the System drive has as little as 22MB while a larger swap file of 1.5x physical RAM to 3.0x physical RAM resides on a second drive (on a seperate IDE channel).

As for your audio card sharing with AGP card, your Mobo book has a list of PCI INTerrupts to outline which slots share resources with other slots (including AGP) - this often includes sharing with integrated devices such as USB and audio.

You made some other interesting points there - particularly about ATI cards. I will look into that... I can sympathise with the PCI Latency issue, too.

Have you heard of software such as NuMark's PCDJ and Native Instruments' Traktor DJ? They mainly thrive on Steinberg technology and Creative's ASIO drivers... There are some other packages out there that are based on the same engine. I am not sure which was the first...

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Bump and please feel free to add your thoughts and ideas.

Any questions already answered in this thread will be split and a new thread will be created.

Cheers.
Marcus.

[sangram]

Evaluating speakers.

How do you properly evaluate and compare speakers before making that buying decision?

1. Placement: is basically everything. A sub placed close to a wall or corner will sound boomy. It can also help a weak sub compensate for some of its deficiencies. Satellites or full range should be placed so that tweeters are at ear level. Try a bit of toe-in (point the speaker inwards), toe-out, or a straight ahead position.

Experimentation is key. For the evaluation session, try and replicate your listening conditions. Do you like to leave your table a lot while listening to music? Or are you the gamer that hunches forward to the screen? Or the relaxed movie watcher leaning back with a bag of popcorn? Subtle shifts in the head position cause a marked change in sound, specially in multi-driver systems...

2. Things that are desirable:

Imaging - Basically the picture of the stereo or multichannel image. Can you tell where the snare drum was, and does it come from the same place every time? Thats' horizontal imaging. Vertical imaging is tougher, and most computer speakers can't actually manage it. The ride bells and high-Q percussion comes off the top, and sometimes outside the speaker's soundfield. Drums are a good instrument to evaluate imaging. Imaging will be good within a particular 'sweet spot', the size of the spot is determined by many things including the speakers, the room, and the way the speakers are placed in it.

Transient response - How well does the system reproduce sharp attacks? Does it have power to recover without ringing (a common phenomenon when the speaker overshoots and fails - listen to Counting Crows 'Anna begins' for a very sharp and difficult snare drum, it pierces the ear on a good system, and sounds like an ordinary snare on mediocre ones). Percussion and drums are a good instrument to evaluate transients.

Tonal accuracy - how well the speakers reproduce the original sound. This is mainly subjective, wind and string instruments (Classical guitar, flute are what I use to check) are a good way to figure if the speakers are faithful. Gaming is less demanding in a sort of way, as the sound in games is heavily compressed to start with, and sound in games is part of a bigger experience. Vocals are very demanding, and a good set reproduces vocals well. Try Diana Krall, Tracy Chapman and Mark Knopfler for voices with texture and layers. Pavarotti or the three tenors are good sources too.

Speed - related to transient response, but not exactly that. Refers to the ability of the speaker to accurately follow the original sound regardless of speaker excursion. Example, when the bass drum has hit and a bass run is played at the same time, the speaker should be able follow the bass run even though the kick drum ring is still on, both sounds should be audible... I use Victor Wooten's killer bass tracks to evaluate speed. My Altec MX5021 fail miserably in this test, they just can't compete with a full-range floorstander...

3. Things that are not desirable:

Comb filtering - very nasty effect where the frequencies in the vertical plane cancel each other out. Best experienced by moving head up and down, doing so changes the sound and some frequencies become duller than others. Either you're not in the sweet spot (should move forward or backward depending on where you are) or the speaker suffers from serious comb filtering issues. Only applicable to multi-way speakers and floorstanders. Smaller bookshelves, due to smaller space between their drivers, have less problems in this area, if any.

Overshoot: Very common in small, underpowered bass drivers like we see on a lot of sub-sat systems. Basically the amp loses control of the driver on very demanding passage and the driver cannot return into its original position in correct time. Solution is to look for a more powerful sub, or reduce volume. A good song to test this on is James Taylor 'Gaia', there's a middle passage in the song at about 3 minutes, that can shake the room or throw the woofer across the floor...

One note bass: Common again in computer setups and car setups, where volume of bass is given more priority than its accuracy. Also common in smallish HT boxes with ports, but to a lesser extent. Due to compromised box tuning, the bass of a certain frequency range always comes out louder than the rest of the bass, and bass is not one frequency. If you cannot hear the movement of the bassline, then you are suffering from it - specially at high volumes.

Resonance: Ringing or resonance is caused by faulty drivers, poor cabinet or crossover design, but is mostly due to the property of the driver itself and the failure of the crossover to correct it by damping the resonance. Manifested by a ringing (most common in tweeters) sound that persists after the original sound has disappeared. Resonance can be mechanical (loose grills can be a cause) or electrical...

Diffraction: The emission of sound by sources other than the one meant to reproduce it. Can interfere with imaging, and result in 'spikes' in the frequency response. Caused by sound being reflected off sharp edges in the speaker, like the rims of the drivers, corners of the cabinet, and objects in the acoustic path of the sound before it reaches your ears. Manifested by a spiky response, sometimes unpleasant. May sound overly bright and harsh, but may be a pleasing effect for some.

So, how do you actually make the choice?

1. Take your own music along. Try to carry a variety of music, not just what you listen to. This'll help you understand how the speakers cope with loads. Classical music, though not everyone's cup of tea, is a very harsh test of speakers.

2. Demand time. Don't decide in a hurry. Take your time, switch between different sets, try out at least five minutes for each track to get your ears to get used to the sound.

3. Care for your ears. Don't start with volume tests. Keep bass and treble or EQ controls flat to start with, and add a bit of EQ for your taste, though I wouldn't recommend it. Listen to a set of speakers for 10-15 minutes before moving on. Take a break while the next set is being set up. I don't drink colas or eat anything heavy before auditioning, as burping and gas buildup clogs my ears. But I'm just a little anal about it.

4. Take a friend. Sometimes it helps to share the blame

5. Try and place the speakers as close as possible to your listening position, this may not be possible, but a few pointers would be

a. Tweeters at ear level,
b. Toe-in (5-6 degrees is usually enough)
c. Sub away from walls

Please feel free to add, edit, and subtract. And happy listening for your new speakers!!

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Awesome