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The A1400-8 Amplifier wins a Reviewer's Choice Award from Home Theater Sound!
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| The A1400-8 digital multi-channel amplifier. |
"Not only was it amazingly powerful, but its transparent, open sound was immediately involving, and didn’t lose its appeal over the long term. . . I could easily live with the Axiom as the sole source of power for my reference system. Considering both the quality and quantity of sound that the Axiom A1400-8 provides for $3850, it’s one heck of a bargain."
-- Roger Kanno, HomeTheaterSound.com
Understanding the “0 dB” Setting on Your AV Receiver Volume Control Display
by Alan Lofft
It’s only in the last decade that the concept of “0 dB” as it relates to AV receiver volume controls and playback loudness has become common on AV receivers and AV preamps. Previously, if a volume control had numerical values marked on the receiver’s front panel or shown in a front-panel display, the numbers got bigger as you increased playback volume; when you reduced the volume, the numbers got smaller. It was simple, logical, and easy for anyone to understand. Loud equals big numbers; soft equals small ones.
On current AV receiver/preamps, it’s the negative values of dB loudness settings that are confusing. In fact, it seems counter-intuitive: As you reduce the playback loudness on your AV receiver, the negative numbers grow larger, and when you exceed the “0 dB” mark as you crank up your AV receiver’s volume to extremely loud levels and possible distortion, the positive numbers are tiny: +3 dB, +6 dB, and so on. The confusion occurs because we’ve grown up comprehending that bigger numbers mean larger values or an increase.
After reading this article, however, I think that you'll find the relative values of negative dB settings are actually logical, because in the old days, the settings on AV receiver volume controls were entirely arbitrary and unrelated to actual dB values. So whatever one manufacturer chose to put on the front-panel volume control or display applied only to that particular receiver. For example, one manufacturer might rate his volume control from 1 to 10, “1” being minimum volume and “10” being the maximum. Another might label the control going from 0 to 100.
History
A little bit of history helps to explain how the concept of 0 dB and its negative and positive values migrated from the professional broadcasting and recording environment to consumer audio gear. In the old days, Bell Labs and the broadcast networks came up with the concept of “0 VU” (which stands for Volume Units) to standardize electrical audio signal levels between interconnected radio and TV stations sending programming across the country over telephone lines to affiliate stations. The “0 VU” setting was standardized as a certain voltage into a particular impedance, and in a sense it reflected the perceived loudness of the incoming source signal (not quite the same as “0 dB,” but close enough for illustration). The use of the VU meter in broadcasting and recording was to ensure a strong enough audio signal that was well above any noise, yet to prevent a too-loud signal that might distort or overload any recording equipment or the input circuits of the control consoles in the other radio stations. So long as the station engineers kept the incoming signal levels at or below the “0 VU” indication, they were likely to broadcast or record a nice clean undistorted signal.
0 VU in Recording
In analog tape recording, the 0 VU setting was viewed as the level beyond which the recorded signal might distort or overload the magnetic tape. In fact, 0 VU is 8 dB below a level of 3% harmonic distortion. With recorded peaks hitting 0 VU or slightly below, distortion was kept below 1%, which is generally inaudible with music or programming sources.
Analog signals were nicely manageable because they behaved in an analog fashion: the louder the signal got, the greater the potential distortion and “saturation” of the tape. You could very occasionally let recorded peaks go a few dB “into the red” zone on the VU meter, because it was unlikely that the minimal distortion would be audible. The VU meter was a type of averaging meter that correlated with perceived loudness but wouldn’t register the peak instantaneous voltage of an audio waveform, so allowances for peak levels had to be built into your recording level settings.
By contrast, with digital recording equipment everything stays pristine and clean as you approach 0 dB, and then BANG, at 0 dBFS (Full Scale) and above, you get gross distortion. Digital recorders have peak-reading LEDs or LCD bar-graph displays that actually register the peak voltage of the incoming audio signals, thus recording levels can be adjusted to never exceed the maximum of 0 dB. (In practice, with sloppy operators, they sometimes do, which accounts for some of the grungy sound quality of some modern digital recordings.)
0 dB on an AV Receiver
So how does all this relate to your AV receiver/preamp’s volume control settings? Think of “0 dB” on your AV receiver’s volume display as a kind of “maximum loudness” setting beyond which you may drive the amplifier into audible distortion or “clipping.”
In the May AudioFile newsletter, I described the subjective sense of loudness changes that increases of 1 dB (just barely detectable change in loudness), 3 dB (slightly louder), or 10 dB (twice as loud) trigger in average listeners. On your AV receiver, the dB indications are still relative and you should hear them that way. If your AV receiver’s setting is at, say, -25 dB, and you turn it up to –22 dB, that 3-dB increase in loudness should sound “slightly louder.” Going from –25 dB to –15 dB, an increase of 10 dB, should sound about “twice as loud”. Keep in mind, however, that the relative loudness of your particular speakers and AV receiver settings won’t easily transfer to another listeners’ volume settings, especially if he has different loudspeakers that have different sensitivity ratings. Your listening distance and preferences also come into play. However, for Axiom enthusiasts who own the same model of loudspeakers or speakers with the same measured sensitivity, then the relative dB values on the AV receiver’s display will apply.
You can use your ears and the display readings on your AV receiver to experiment with small or large changes in loudness. With music, are you able to detect a 1-dB increase or decrease in loudness? If you listen really closely, you’ll likely be able to. It’s not easy or readily apparent with music playback, which is one of the reasons that casual comparisons of different loudspeakers or receivers are so flawed. If the playback volume isn’t exactly equal, then you may feel that one speaker or receiver sounds “better” than the other, when in fact one may simply be 1 dB louder than the other. And much of the time, you won’t “hear” the slightly louder one as being louder; you’ll just sense that somehow it seems more pleasing. Once you precisely adjust the playback levels with pink noise and a Sound Pressure Meter, many alleged differences you thought you were hearing disappear. Credit the decibel and a Sound Level Meter with keeping things honest in listening comparisons.
Q. Sir, I come from India. I am not an engineer but your articles are a pleasure to read as they are easily understood. My congratulations to you for doing a great service to audiophiles the world over. A specific question here: I have a Sony STDR DE 598 Receiver. It has dts as well as Dolby ProLogic II decoders, and I have matching 5.1 speakers. However, since I play only old '50s, '60s, and '70s recordings that are mostly monophonic, mastered from studio open-reel tapes or vinyl records, I want to know whether it is a better option to have an old fashioned analogue amplifier for playing such records? How can I get the best from this receiver? A second question: why do vinyl records, even the scratchy ones, sound more faithful to the original voice and instruments than a digital recording? I can't resist playing my old vinyl collection. What is the option for me to connect a tuntable to this receiver which does not have a phono jack? Also, what budget models of turntables would you recommend? I shall be grateful for an early response. -- B.P. Bagchi
A. There would be no particular advantage to using a vacuum-tube amplifier to
play back your older monophonic recordings unless you feel that the "tube
sound" that some enthusiasts prefer may cover up some of the older
recordings' problems. Tube equipment tends to generate more distortion than
your current Sony would, but the even-order distortion from tubes tends to
impose a kind of pleasing "wash" to musical playback. It is not more
accurate--it is less so--but older recordings vary dramatically in sound
quality so it may be preferable to "conceal" some of the flaws behind a
scrim of pleasing harmonic distortion.
Your second question is hotly debated world-wide on forums like Axiom's as
well as other music and audio-related web sites. Since I grew up with mono
vinyl recordings (even 78 rpm discs when I was little), I can tell you that
there are hundreds of really awful sounding vinyl records and plenty of very
good ones. Similarly, there are hundreds of poor, strident,
aggressive-sounding digital CDs as well as many wonderful CD recordings. I
still have a large collection of vinyl LPs, however, I rarely play any of
them, mainly because I can't stand surface noise and I also dislike the
inherent distortion that is quite audible sometimes towards the inner
grooves of a disc, especially when large classical works get loud. By
comparison, digital recordings--the good ones--are entirely free of any such
distortion and of course there is no surface noise to intrude on the music.
Vinyl enthusiasts and CD fans will never agree. You may simply prefer the
sound of analog recording and playback. Likewise, I love the much greater
dynamic range, extended deep bass, and undistorted dynamics that a
well-engineered CD and digital recordings will deliver.
To use a phono input with your Sony, you'll need to get an accessory
moving-magnet preamp. These are available for around $100 or less. Your
turntable connects to the outboard preamp, and then you connect the preamp
to any of your audio inputs on the Sony.
There are a number of quality belt-driven turntables available that sell
around $300. Look for the Pro-Ject Debut III ($299US) or the Music Hall
MMF-2.1 ($349). One other brand you might consider for is Rega. The latter and
Music Hall are British brands, and they are also available online from
www.musicdirect.com
If these models seem too expensive, you should check out inexpensive
direct-drive models from Stanton, which sell for about $150. The tonearms on
the Stantons may not be as refined as the British brands, but for your older
mono LPs, they would be entirely satisfactory.
Try Googling "magnetic phono preamps" as well. You may find some phono
preamps selling for very high prices. There is no need to pay huge amounts.
They won't sound any better, however paying more may buy you a quieter preamp with no audible noise. The circuitry of a phono preamp is fairly basic
and you should find one in the $75 to $150 range that will do everything you
need. -- A.L. |
