Audio Myths

1. Audio Myths And Critical Gear Evaluation

2. Agenda • Evaluating Gear • Design of experiments to properly evaluate gear • Goal: Let you invest your money in the right places • Avoid enriching scam artists. • Get better sound, improve your recordings. • Audio Myths • Popular beliefs that everyone “knows.” • Discussion of some audio scams (?) ($1200 AC power cord, oxygen-free copper, directional cables, etc.) • Discussion of why some things like cables MAY make a difference.

3. Lavry Distressor Section 1 Purple MC77 Gas Powered Blender Evaluating gear Avalon M5

4. An Experiment • Bob borrows a “hot” new preamp that his friend recommends for accordion polkas. • He sets up a mic and records 10 seconds of accordion polka with the new preamp. • He then switches preamps, sits back down and records the same passage using the new preamp. • Bob confirms that the new preamp sounds way more open with better transients and less veiled top end. He spends $2000 for the new preamp. • (Accordion polka still sucks.)

5. A good experiment? • What did Bob do right or wrong?

6. A poor experiment • 1. Mic position and performance variation from take to take can mask the subtle differences between preamps. • 2. No level matching- Louder sounds better to most people. • 3. Expectancy effect. • 4. Experimenter bias. • 5. Accordion Polka

7. Expectancy Effect(When what YOU expect influences outcome) • Expectancy effect was discovered by Rosenthal and Fode (1963) and is a great example of experimenter biasUsing, an independent group design, they got two groups of students to train and look after two groups of rats. One group were told they had 'bright' rats, the other 'dull'. In fact there was no difference at all in any of the rats intelligence. Rosenthal and Fode made this up. (Not sure about the students’ intelligence differences.) The students than had to time their rats performance running a maze. The bright rat group produced data that indicated their rats had learned to run the maze quickly. The dull rat group produced data that indicated their rats had learned to run the maze slowly. Rosenthal and Fode concluded that their students (false) expectations of their rats ability had an effect on the overall results. • Another example of the observer-expectancy effect is demonstrated in music backtracking; some people expect to hear hidden messages when reversing songs, and therefore hear the messages, but to others it sounds like nothing more than random sounds. Other prominent examples include facilitated communication and dowsing.

8. Expectancy Effect

9. Experimenter Bias(When what the experimenter expects influences outcome) • In another experiment a group of students was told to survey residents of a town about whether another nondescript nearby town was a good place to live or not. (Not San Francisco and Oakland) • They were given a script of questions to ask and told not to deviate at all from the script. • Half the surveyors were told that most people thought the nearby town was an undesirable place. The other half that it was a very desirable location. The interviews were recorded to ensure that there was no deviation from the script.

10. What Happened? • Even though the surveyors never deviated from the script, those that were told that most residents considered the nearby town to be undesirable got that result in the survey, and those told it was desirable got that result.

11. What does it mean? • Humans are great communicators, verbally and non-verbally. • If your buddy thinks that a preamp is great and asks you to have a listen to two tracks “blind” there’s a good chance you will pick the track that he likes even if he doesn’t tell you which is which. (Or if you think he’s a complete moron when it comes to gear you might pick the opposite track.)

12. Proper Test DesignFIRST, MAKE SURE YOU CAN HEAR A DIFFERENCE! • A good test controls as many variables as possible. • Pick an appropriate test sample. Highly compressed metal isn’t the best sample for evaluating reverb tails. • A good test is “double-blind” meaning neither the listener or the operator knows which track is which. • A good test is statistically significant. If you listen only once in an A/B test you have a 50/50 chance of guessing a particular outcome.

13. Audio Testing • A/B/X tests • Play track 1 followed by track 2 followed by a random (double blind) selection of track 1 or 2. • Decide ahead of time how many trials to do. More trials means more confidence in results.

14. Software that makes it easy • Create 2 WAV files • Load files into automated A/B/X tester • Tester will play file A, file B, then a random choice of A or B. • Subject chooses response for each test. • This is easy and will tell you without bias if you can hear differences in the files.

15. There are several free A/B/X programs • WindowsWinABXABC/Hidden Reference Audio Comparison ToolFoobar2000 (audio player with ABX option) • (Possibly they could have picked a better name?)LinuxLinABX

16. Demo of ABX Software • SM7 & AT4060 comparison • Microphones capsules placed at identical spacing from source. Samples recorded simultaneously. • Samples matched for level. • Loaded into Foobar 2000. • 5 Trials • In this case the mics were relatively far from the source, and an intentional defect is present to demonstrate the method.

17. Probability Chart

18. The Null Test • Helps determine if two audio files are identical • Use in evaluating plug-ins, DAWs, processing algorithms, etc. • Create two tracks in your DAW with the same source material. • Flip the polarity of one of them. • If you hear anything on playback the files are NOT equal. • If you can’t hear anything for all practical purposes the files are identical.

19. Q: How many audio engineers does it take to change a light bulb? A: Five. One to tell the intern to do it and four to reminisce about how much better the vintage bulbs were. Section 2 Audio myths

20. MYTH (?) #1 • Recording at 24 bits is a HUGE improvement over 16 bits. • Let’s find out: • We need some critical material with lots of dynamic range and maybe some reverb tails we can listen to. Acoustic guitar is a good choice. • We can record at 24 bits and dither down to 16 bits, then compare both files. • We’ll also compare 2 files recorded independently at 16 bits and 24 bits.

21. A/B/X Example #2 • Acoustic guitar at 16 bit vs. 24 bit resolution • Acoustic guitar recorded at 44.1 kHz & 24 bits with MK012 SDC through SCA J99 preamp and Lynx Aurora converter. • File dithered down to 16 bits (NO dithering). • A/B/X comparison, 10 tests.

22. A/B/X Example #3 • Acoustic guitar at 96kHz sample rate vs. 44.1kHz sample rate. • Acoustic guitar recorded at 96 kHz & 24 bits with MK012 SDC through SCA J99 preamp and Lynx Aurora converter. • File resampled down to 44.1 kHz. • A/B/X comparison, 10 tests.

23. The Null Test

24. $$AC Power Cord$$Does it make a difference? • OyaideTunami GPX-R • OyaideTunami GPX-R • PCOCC-A copper with Triple copper foil, and carbon shielding, terminated with Oyaide Gold/Palladium plugs, the sound character is is more forgiving than its Acoustic Revive Counterpart, the Power Reference against a dead-silent background. Price is for a 2 meter length.Sku # : Oyaide-Tunami-GPX-R Manufacturer : OyaideOur Price : $495.00 Qty : * Item comes in a set of 4

25. Does it pass the common sense test? • There are 200 ft of plain old copper ROMEX between the outlet and your breaker box. • There are miles of plain old copper cable between your breaker box and the power company. • There is lots of printed copper PC board inside your gear that’s just plain ordinary copper. • A modern AC/DC power supply is designed to convert anything from 90VAC to 264VAC to (for example) 5V and 3.3V while rejecting any disturbance on the AC line. AC power is dirty. A better cable will just transmit the noise and spikes more effectively to the power supply. There’s no magic filtering in these cables. • Better shielding can reduce radiated EMI, but 60Hz hum comes from the power line and conducted EMI comes through the cable anyway. • Modern audio circuitry further rejects any disturbances on the DC supply. • Doctors looking for the most minute EKG or EEG signals don’t bother with special copper, line cords, etc.

26. Hard to see how it could make any difference. • If you are convinced it does, do a well-designed controlled A/B/X test. If you can reliably pick the expensive cord over a $4 cord there’s no argument. • If you are convinced it does and you don’t want to do an A/B/X test see me after the presentation because I have some special mic cables for sale for only $2950.00

27. Monitor/Mic CablesDo they make a difference? • At audio frequencies, a cable has several parameters that can make a difference in sound. • Resistance: The resistance to the flow of electrons or signal. • Influenced by the material, conductor diameter, length of cable • Skin effect makes the effective resistance higher at higher frequencies • Capacitance: Can act with resistance to low pass filter a signal. • Influenced by the insulator, conductor spacing, geometry. • Inductance: Can cause peaking or band-pass filtering with capacitance. • This is almost always negligible under normal circumstances. • Shielding • Braid is best, foil can be OK. Helps reject external electromagnetic fields (e.g. hum.) • Construction: Tightly twisted conductors allow balanced connections to eliminate interference. • Connectors • Plating on the contacts can affect contact resistance and lifetime. Contact material can affect contact surface area causing high resistance connections.

28. What do you think? • Silver cables? • Cable break-in services? • http://www.morrowaudio.com/breakinservice.htm • $485 Wooden knobs for gear? • CD demagnetizers? • Altmann Tube-O-Lator Lacquer • The ALTMANN “TUBE-O-LATOR" lacquer is applied only on the top surface of plastic semiconductor packages of AD-converter-chips, DA-converter-chips, OP-amps and discrete transistors. After application, the overtone spectrum of these active devices changes immediately and permanently. The new sonic signature will be natural, full and tube-like. The ALTMANN “TUBE-O-LATOR" lacquer electromechanically balances the resonance-spectrum of the plastic chip package and semiconductor itself in such a way, that a natural sounding overtone- spectrum of the treated active device will be generated. • Audioprism CD stoplight pen • Color the edges of your CDs to improve sound • Shakti Stone • "I put the stone on the center of my CD player, and played the same track. Lo and behold, I was transported to yet another dimension of resolution. I suppose the best way to summarize the most beneficial effects of the SHAKTI Stones is to say that they added smoothness to my system."

29. Questions?More from AES video? Q: What’s the difference between an accordion and a trampoline? A: No one takes their shoes off to jump on an accordion.

30. Backup Material

31. Skin Depth • The skin depth of copper at 20kHz is about 0.47mm, and for the resistance of the wire at 20kHz to be double the d.c. value the radius must be 1.4mm. (This applies to solid core wires, and for lower radius wires the skin depth gives a lower relative increase in resistance, and so is less significant.) The d.c. resistance per metre is about 0.0028 ohms, so the 20kHz resistance is 0.0056 ohms, half of this contributed by the skin effect. • To take an extreme example, suppose 10 metres of this wire is used in a speaker cable to drive a speaker with impedance as low as 2 ohms at 20kHz ( fortunately very rare ). The cable will have two conductors giving total added skin effect resistance of 0.056 ohms. In series with the 2 ohm speaker resistance this gives attenuation by a factor 0.97, i.e. -0.24 dB. It has been claimed that response changes around 0.2dB are just audible in direct comparison at lower frequencies, but a variation of 2dB or more may be needed at 20kHz, and so 0.24dB is of no significance. (Few speakers are flat to within even 3dB up to this frequency.) For most speakers with impedance well above 2 ohms at 20kHz, and using cable lengths much less than 10 metres, even 1mm diameter is usually more than adequate as regards added skin depth resistance, though the d.c. resistance may be a little excessive for long cables, being around 0.04 ohms per metre total for the two conductors.