Signal to noise ratio is the end all and be all

Mar 7, 2024
I suggest the path to the best sound is to attain the highest signal to noise ratio (SNR). We commonly pursue this within our electronics, but I believe it extends well beyond this, culminating not in what comes out of the speaker, where I think many folks stop, but rather in what finally hits our ears. In my view SNR applies to all signals, not just electrical, and I regard wave interference in the listening room as one of the largest noise contributors. Perhaps emphasizing the term waveform rather than signal would be helpful. I regard them as synonymous.

To expand, in the analog audio world the signal exists as a waveform. The original acoustic waveform hits a microphone that transduces this acoustic signal into an electrical waveform. For recorded music, this electrical waveform is then transcribed into bits in the digital world, a physical groove on a record, magnetic energy on a tape. Our various devices (DAC, phono cartridge, tape head) convert this stored version back into an electrical waveform. In the vinyl world, we further address signal purity by isolating phono cartridges, platters and tonearms to avoid extraneous influences that would change the way the stylus is able to faithfully retrieve and convert the information from the signal embedded in the groove, thereby maintaining the SNR

Once acquired, we diligently maintain the purity, accuracy, integrity of this electrical waveform from tapes, records and DACs via equipment topology, vibration isolation, electrical isolation with dedicated circuits, fiberoptic cables, cable hygiene, and power conditioners. Anything that adds, subtracts, disrupts, distorts, colors or otherwise interferes with the original waveform can be considered to lower the integrity of the original waveform/signal, either by increasing the noise or decreasing the signal. The best audio system in the world cannot leave the original electrical waveform unchanged. The electrical SNR always suffers, but the better the system, the less the damage. You know the advertising terms, “vanishingly low distortion” and “highest signal to noise ratio”. This is otherwise known as retaining the original waveform.

These electrical waveforms that our sources have recreated ultimately reach our speakers and are transduced back into an acoustic waveform. This includes waveforms associated with the fundamental wavelengths of the instruments and voices and their harmonics, the resonances and related acoustics of the recording space and even the occasional contribution of a cough or a truck rumbling by. These all comprise the waveform/signal coming out of the speaker. At this point, the signal can be regarded as having a very high acoustic SNR since there is not yet any room-associated noise interacting with the signal/waveform. This may be a reason headphones and near field listening are preferred by many.

Once it leaves the speaker, this waveform, the original signal, makes a beeline to our ears but it also travels to every wall and corner of our room where it is reflected and after a while, makes it to our ears as well. When reflected waveforms are relatively loud and hit our ears within the window during which we cannot distinguish their arrival time from the incoming original waveform, they become the noise that competes with the original signal/waveform and consequently lowers the signal to noise ratio. Reducing these competing waveforms in number or amplitude through absorption or diffusion will increase your SNR. You do want to retain some reflections for a sense of space and ambiance so pure absorption is not indicated. You just want fewer or softer competing waveforms (noise) so the original waveform (signal) predominates. In a related vein, speaker isolation footers/stands and stiff cabinetry enhance non-electrical SNR by ensuring the acoustic waveform from the driver is created only by the electrical signal and not by physical vibrations rattling the driver and creating extraneous and competing waveforms.

Before I had my dedicated room, I would rearrange the living room furniture when my wife was away and place freestanding 2x4 acoustic absorbers at the first sidewall reflection points for extended listening sessions. This simple addition made a huge difference and made me a believer. Over the last few months, I have added room treatments that together cost more than any one single component in my system. I initially paid attention to first reflections with absorption on the walls, ceiling and floor. I also directed my efforts towards speaker boundary interference response with appropriate placement of the speakers and listening position. Bass traps and a distributed bass array dealt with uneven lower bass response. Not wanting to dull the room with overabsorption, I added pure diffusion or a combination of diffusion and absorption.

What I now have is a system that not only provides a very accurate signal, but one that is not muddied by all of the other signals (noise) bouncing off the room surfaces. Instruments and voices are clear with an obvious start and stop. While the system always had decent width and height, they are greater now. One of the more obvious contributions is that the soundstage extends in front of and far behind the speakers. On a good rock recording, I can place the drum set, the bass, the keyboard, the vocalists and the guitars three-dimensionally. Classical and jazz are even more remarkable. It is stunning and at times, even startling.

I recognize that not everyone has a room they can devote to their audio pursuits, but within your means and what you and yours find socially acceptable, you should do everything you can to attend to the noise your room adds to your otherwise pure and pristine signal. I believe fuses, power cords, cables, amplifier design, speaker type, etc., all pale in comparison. If you think something is interfering with any of your waveforms/signals before they reach your ears, fix it if you can. Any wave, anywhere. Source, electronics, speakers and perhaps most significantly, your listening room. You have paid good money and paid close attention to the SNR up to the point the signal leaves your speaker. Why stop there? Defend and protect your hard won signal from all the noise throughout the entire reproduction process. Everything counts, including the room.
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Just a nitpick on terminology.

I think the term "noise" in a signal-to-noise computation is based solely upon the added data in the output that is not a function of the input. So, the noise floor of a preamp in your electronics chain, or the refrigerator or HVAC in your room.

Any unintended change in the output which is a function of the input would be referred to as distortion (non-linearities), and not noise.
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Very nice, Mr. Roominator, but there are two significant sources of noise you haven't addressed.

1. Speaker cross-talk. Sound waves from the left speaker arrive at your right ear after a slight delay due to the path length difference. Simultaneously, sound waves from the right speaker arrive at your left ear after a slight delay. It’s up to your brain to sort out those different signals and their sources to create a realistic sonic picture. The problem can solved with a soundproof, floor-to-ceiling barrier installed in the space between your nose and the midpoint between the speakers to eliminate cross-talk. Alternatively, use ambiophonic DSP to digitally remove the cross-talk.

2. Dither, which is random noise added to digital recordings to mask quantization noise. The magnitude of quantization noise is ±½ LSB: The magnitude of old-school dither is ±1 LSB. Modern, noise-shaping dither is much larger. Although dither is nearly inaudible, when you have a fixed dynamic range, defined by the sample width, every bit that carries dither noise is one less bit that carries the signal.

Conventional wisdom says dither is necessary and cannot be removed. That's true for pure, steady-state, single frequency sine waves, but not sound originating in a live acoustic space and recorded with microphones. In that environment there many sources of random noise that mask the quantization noise. You've got the ambient noise of the venue, the self-noise of the microphones and the electronics between them and the ADC, the beating hearts and breathing of the musicians, to name a few.

Lately, I've been experimenting with ways to remove dither from CDs. It's not difficult once you realize random noise cannot be resampled. My first attempt was to resample a CD track to 2,822,400 and then to 176,400 for my AD1865 DAC. For me, hearing a 'dither-free' CD track was a revelation. The process is easy to do using foobar and two instances of the sox resampler plugin. I've since moved on to a custom plugin that allows greater experimentation to remove the last hint of dither noise that remains.
Pictures or it never happened!
I suggest the path to the best sound is to attain the highest signal to noise ratio (SNR). We commonly pursue this within our electronics, but I believe it extends well beyond this, culminating not in what comes out of the speaker, where I think many folks stop, but rather in what finally hits our ears. In my view SNR applies to all signals, not just electrical, and I regard wave interference in the listening room as one of the largest noise contributors. Perhaps emphasizing the term waveform rather than signal would be helpful. I regard them as synonymous.
Can I suggest that noise and distortion in what we hear comes from sources that aren’t even in the signal path? How’s that for a revolutionary statement? What I mean here is that our hearing is not simply the process of our ears, neurons and brain converting acoustic waves to music, the standard (and archaic) interpretation.

It’s actually rather straightforward to show that things in the local environment influence the final sound we hear. Examples are CDs and LPs in the room. Removing them improves the sound. it’s as simple as that. Same goes for videos in the room. And books. Yes, I realize space is limited. Also, barcodes! All barcodes hurt the sound. So, either remove them, cut them off or draw a red line through them. Unused electronics, cables, musical instruments, they all are bad for the sound. The less you have in the room the better the sound. I know what you’re thinking, “But I‘m not taking my room treatments out!” :)

So, the Actual SNR - the one we hear - is determined by a great many factors, not only by the aggregate of noise and distortion in the system per se.
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