RIAA Audio Standards

[moamps]

In the good old days +/-75kHz was the limit.

In my country still is.
Channel (station) separation is 200kHz.
Professional FM receiver has +4dBm output for 75kHz deviation with 400Hz typically.
In audio dBm ultimately is 1mW/600ohm=0.775V.

On the other hand, for commercial reasons, many stations want to sound as loud as possible. That is why they use terrible multiband compressors and clippers to increase the perceived loudness while still complying with the spectral requirements.

Oupsss. Terrible compressors are single band. "My" old ORBAN OPTIMOD-FM 8100A/XTA isn't. There is more reason then "only loudness" for using smart compressors.

Regards

 

[tubetvr]

Didn't I say "in the RF world"???????????

Yes you did but in the RF world it is quite normal to have other impedances then 50 ohm like 75ohm. 0 dBm is 1 mW regardless of what impedance you are using.


Regards Hans

(working in RF design since 1983)

 

[PGW]

Just to get back to the thread for a moment

A nominal output from an RIAA-equalised preamp may be (say) 0.5V rms at 1 kHz. How are you performing this equalisation?

It's worth bearing in mind that the 'raw' signal before equalisation is 10 times larger at ~20kHz than it is at 1 kHz, and 10 times smaller at 50 Hz. Does your preamp need to handle these 5V rms signals prior to equalisation? What 'headroom' for transients and peaks will you need?

A general question regarding the RIAA equalisation: the upper tine constant in the RIAA spec is 75 microsec = 2121 Hz: the filter just carres on forever beyond this. I read somewhere recently that adding a zero in the response at ~37.5 microsec, to counteract the RIAA low-pass action at ultrasonic frequencies yields better audio performance.

Any comments, supoortive or otherwise, of this assertion?

-- John

 

[EC8010]

Re: Just to get back to the thread for a moment

Does your preamp need to handle these 5V rms signals prior to equalisation? What 'headroom' for transients and peaks will you need?

Yes, but sometimes it's hidden. It all depends on the gain structure of the individual pre-amplifier and the way that the equalisation is implemented. If NFB is used, we need current rather than voltage headroom. Delivering current with little voltage is equivalent to a vertical loadline, so distortion rises before feedback. Altenatively, passive equalisation can be used. Because of the 20dB (1kHz) loss rwequired by passive equalisation, it is difficult to satisfy noise and headroom requirements simultaneously. One solution is to split the equalisation, and do 3180 and 318 in one stage,and 75 in another. These stages can be active or passive, or a combination of the two.

A magnetic cartridge is a velocity transducer. It's output rises at 6dB/octave with frequency. If you apply a transient to it, you can expect a lot of HF energy (particularly with moving coil cartridges where the stylus tip mass/vinyl resonance is quite pronounced). The most common transient is dirt or a scratch. There is no such thing as too much headroom in an RIAA stage.

 

[mrfeedback]

CLICK, Or click.

A magnetic cartridge is a velocity transducer. It's output rises at 6dB/octave with frequency. If you apply a transient to it, you can expect a lot of HF energy (particularly with moving coil cartridges where the stylus tip mass/vinyl resonance is quite pronounced). The most common transient is dirt or a scratch. There is no such thing as too much headroom in an RIAA stage.

Yes, very true.
A bad sounding phono pre-amp emphasises surface noise, and good sounding ones do not.
Good sounding preamps filter the HF stuff first and have relatively high voltage supplies to ensure adequate headroom throughout.

Eric.