Originally Posted by CraigNZ
The reason I am asking about the output level of the AVM60 is because I am currently 'matching' the output of the AVM60 to the input of my amplifier in order to achieve maximum dynamic range in the signal chain. The specifications say the maximum output of the AVM60 out of the RCA connectors is 4.2 Vrms. The input sensitivity of the amplifier is 0.9 Vrms. Using an online calculator it shows I need to insert a 16 dB attenuator at the input of the amplifier to match the two components. What this means then is the maximum output of the AVM60 cannot overload the input to the amplifier. It also means the noise added to the signal when traveling over the interconnect cable between the two components is also reduced by 16 dB resulting in a quieter signal.
But the effect of this is now the audio level coming out of the speakers is also reduced by 16 dB for a given volume setting on the AVM60. So when previously listening to music or a movie at -20 dB on the AVM60 remote, I now have to change that to -4 dB to bring the volume back up to what I am used to listening to. Which means not a lot of room left to increase the volume. Then I discovered I could get an extra 10 dB from the AVM60, but is it clipping the output of the AVM60 when I do this?
Where this is important is in the dynamics of the source signal. I would not listen to music or a movie at full volume, it would be way too loud. But in the music or in the movie audio track there are dynamics which can momentarily produce a spike of 20 dB or so, for example a rim shot on a snare drum or a gun shot. Assuming the source signal is PCM then the source material will accurately reproduce the recording (assuming of course the microphone and mixing stage did not clip the spike). And assuming the AVM60 (with ARC correction turned off) correctly reproduces the spike then a large signal (> 4 Vrms) could come out of the AVM60. If that were input to the amplifier with no attenuation, the spike would clip and sound distorted coming out of the speakers. This is why it is important to match the preamp to the amp, which is done all the time in professional setups. This all assumes the slewing rate of the amplifier can match the AVM60 slew rate.
So back to my question, if a spike in the source jumps the signal to 0 dBFS, what is the output level from the RCA connector if the volume level is set to +10? If it is 4.3 Vrms then it means no clipping on the output and I then have an extra 10 dB to work with out of the speakers.
Referring to my earlier posting above, I decided to get an oscilloscope and make the measurements myself. The scope hass two channels so I put CH1 on the output of the Right Channel RCA connector and CH2 on the output of the Left Channel RCA connector. I then used REW on my PC to create a 1 kHz sine wave signal at -0.1 dBFS level. The signal was passed over an HDMI cable to the input of the AVM60. With room correction turned off and the volume control set to 0 dB I measured the voltage as 2.96 Vrms on CH1 and 3.06 Vrms on CH2. This is interesting because an earlier post on this forum stated the output of the RCA connectors was max 4.2 Vrms. But, if I measured 3.0 Vrms (average of both channels) then the "Peak" voltage is 4.3 V. So I am thinking the value given on the post should have been "Peak" voltage, not "Vrms". This then matches what I measured on my system.
Next, given the maximum signal input to the AVM60 (0 dBFS) what happens to the output of the RCA signal if I now increase the volume on the AVM60 from 0 dB to +10 dB. Well, it clips .. no surprise there. In fact, any positive volume level results in a clipped signal going to the amplifier. So as long as your input signal is less than -10 dBFS then you can push the volume on the AVM60 past 0 dB. Not being able to determine this while watching a movie or listening to music I would recommend not to raise the volume of the AVM60 above 0 dB. This can be done in the AVM60 setup screen (General settings).
It is also interesting that to bring the output of the AVM60 at maximum volume (3.0 Vrms) down to the input of my amplifier (0.9 Vrms) that I need an attenuation of 10 dB at the amplifier. If I do this then I accomplish two things: a) there is no way the AVM60 output can then overdrive the input of the amplifier, meaning no clipping of the audio to the speakers, and b) I reduce the noise added to the signal from the AVM60 to the amplifier by 10 dB, which provides a much cleaner signal.
Also, there is a lot of articles on the Net about whether the signal from the preamp should be attenuated to match the amplifier input. The general consensus is to set the output of the preamplifier at 10 dB above the input sensitivity of the amplifier, referred to as "10 dB overlap". This "overlap" is a compromise between high signal-to-noise at low listening levels and low distortion at high listening levels. This appears to be what Anthem did with the AVM60. But what is missing in the decision is "transients", e.g., a gun shot when watching a movie, or a cymbal crash when listening to a orchestra. If the transient exceeds the overlap boundary then it will clip and you will get distortion. To me, the best dynamic range is achieved when the "overlap" is set to 0, meaning the output of the preamp is attenuated to match the input sensitivity of the amplifier.