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Topic: The RIAA curve? (Read 4815 times) previous topic - next topic
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The RIAA curve?

Hello HA,

I was recently perusing an electronics catalog for components and came across the amplifier kit section that praised its own amps for properly implementing the "RIAA curve" for phonograph input.

Has anyone ever heard of this?

According to the description in the catalog (I'll have to paraphrase a little), modern amplifiers playing vinyl sound dull and flat because of their flat frequency response -- that's because vinyl is (purposely?) not encoded with the extreme highs and lows of the audio spectrum. So, their pitch for selling their amps is taking into account this so-called RIAA curve.

In a way, it makes sense. If the intention was to maximize the fidelity of audio on vinyl by limiting the amount of low and high frequencies, then the adjustment can be made through conventionalized hard EQ-settings.

Now the world of phono preamps becomes more mystifying. The whole time I thought phono inputs were unique because of impedance-matching. Now it appears there are some preamps the adjust the EQ to a RIAA compiant standard. This brings up a lot of interesting questions about the quality of phono preamps, the vinyl mastering process, the argument of whether vinyl sounds better as a medium (without the EQ adjustment), the effective frequency response of vinyl vs. the optimal frequency response, etc.

Let me rekindle the analog vs. digital debate by saying that any medium that gets an EQ adjustment will sound "better" to most listeners. Not to mention, at least the RIAA has a standard EQ for vinyl if not a standard of loudness for CD
"Something bothering you, Mister Spock?"

The RIAA curve?

Reply #1 –
Plain and simple ... the RIAA curve is applied to the audio signal prior to cutting the original stamper that is used for vinyl production.

Basically, the whole spectrum's volume is lowered (which also lowers vinyl's max. dynamics or SNR) while the low-end receives additional lowering treatment.

The physics behind this is to lower the signal amplitude - especially high bass amplitudes (because in general, a music spectrum follows a 1/f amplitude function) to be able to a) maintain a small groove distance on the LP (for playing time ... high amplitudes would render that impossible) and b) avoid potentially damaging stylus amplitudes during playback.

The way that treatment had to be performed was defined in an RIAA standard which quickly became an international recording standard.

Amps with phono input do nothing more than applying a mirrored RIAA EQ curve to the incoming signal after specific amplification (for MM/MC/HighMC) and cartridge capacity matching (few amps allow that these days).

Any amp whose phono input is not properly aligned to the RIAA standard will sound either too thin or too fat, regarding bass frequency response.
The name was Plex The Ripper, not Jack The Ripper

The RIAA curve?

Reply #2 –
There are actually two components to phono equalization. The more significant of the two is compensation for the phono cartridge response, which is proportional to velocity rather than displacement. If this were not compensated then high frequencies would be much louder than low frequencies, with 20 kHz being 1000 times louder than 20 Hz of equal amplitude in the grooves. Typically the low frequency boost that compensates for this effect is rolled off at around 20 Hz, so as not to amplify rumble too much.

The other component, the RIAA compensation, boosts the high frequencies as recorded in the grooves. This is because high frequencies are generally much lower in amplitude in recorded material than middle frequencies so you can boost them without exceeding maximum groove displacement. When this is compensated on playback it has the effect of reducing high frequency noise.

The RIAA curve?

Reply #3 –
Every phono preamp applies the necessary inverse RIAA compensation. This is one of the preamp's three main jobs. This is a task that was conquered 60+ years ago. How to do it is very well know, and is easy for any competent preamp designer to get right. Of course, many manufacturers make claims that their implementation is somehow better than anyone else's; they all want you to buy their product, but the differences will be one of those aspects that somehow evaporates under ABX testing.

The RIAA curve?

Reply #4 –
Quote from: AndyH-ha on
Every phono preamp applies the necessary inverse RIAA compensation. This is one of the preamp's three main jobs. This is a task that was conquered 60+ years ago. How to do it is very well know, and is easy for any competent preamp designer to get right. Of course, many manufacturers make claims that their implementation is somehow better than anyone else's; they all want you to buy their product, but the differences will be one of those aspects that somehow evaporates under ABX testing.


Not every difference evaporates w/ABX testing. Generally some accepted distortions to the signal, when measurable, are acknowledged on both sides of the debate.

It is obvious that these measurable distortions are found in some amplifiers, some preamps, and almost all current phono preamps. Nobody cares about this circuit nowadays. If you don't want to spend money, buy an average quality component from the 70's and do an ABX!

I have yet to see any highend company claim something different is done compared to other competent designs other than tweaking with admittedly diminishing returns. There's no snakeoil here.

The RIAA curve?

Reply #5 –
The RIAA EQ is defined, it is specific. While there are various ways of implementing the inverse RIAA that must be applied on playback, the goal is always the same. The results can be measured. One can say with reasonable certainty that compliance is withing ± 1dB or ±0.1dB, etc. to the limits of test equipment.

Some preamps may do a better job that others, but doing the job to better than the limits of human hearing isn't that difficult and is normally implemented correctly. Maybe some of the really low ends products don't bother, probably by using components (capacitors & resistors mainly) with too wide tolerances rather than through actual bad circuit design.

The phono preamp does more than just apply the EQ. There is more room for differences between products in other parts of the circuit, but that wasn't the topic of the thread. I admit I haven't auditioned any $12,000 or $60,000 phono preamps, but I really suspect that snake oil is getting into the works there.

The RIAA curve?

Reply #6 –
Quote
modern amplifiers playing vinyl sound dull and flat because of their flat frequency response


What a load of junk!

If anyone was stupid enough to miss the RIAA EQ from a phono input, the result would be a horrible shrill hissy screechy mess.

Cheers,
David.