John Curl's Blowtorch preamplifier part II

[john curl]

For the record, 'resistive' Z out, over frequency means two things: One, that the open loop bandwidth is high. Two, that the output coil has either been removed or is very low inductance. These are both good things, in my experience.

 

[Joachim Gerhard]

Most conventional loudspaekers have an inductive rise in the treble anyway. A long cable with very high capacitance and very low ohmic resistance can make trouble though with certain amplifiers. I was always wondering how an amplifier should be designed at the output interface that gives very good results with all kinds of cables and loudspeakers.
I think no universal Zobel or Output Inductor can do that.

 

[john curl]

I personally have found no real problem with a simple Zobel network on the output consisting of a good film cap and a series resistor. However, I have not looked into it as extensively as Charles Hansen (of Ayre) has, and he has found them problematic.
However, if you just look at the ratio of the output impedance of the amp from low frequencies to 20KHz, you will find big differences. Usually, the least difference is best.

 

[jan.didden]

Well, I asked a question about a measurement, why those values would be better than others.
So far I've got "in my experience", "I think", "obviously" and a couple of similar 'arguments'.
Maybe I was expecting too much

jd

 

[myhrrhleine]

something often overlooked.
it might be the 'betweenness' that we easily hear.
maybe it's inbetween sample amplitude 32,768 and 32,769 that matters.
how many analog values are there inbetween?

 

[Joachim Gerhard]

You can artificially put some in between with a spline algorithm.

 

[john curl]

That is the problem, people think that we are getting 16 bit resolution of material that is 40-60dB down from the operating level. The bits are not there.

 

[PMA]

Makes no help for resolution.

 

[SY]

something often overlooked.
it might be the 'betweenness' that we easily hear.
maybe it's inbetween sample amplitude 32,768 and 32,769 that matters.
how many analog values are there inbetween?

Quantization distortion is very, very well known. That's why we use dither and the anti-imaging filter.

 

[PMA]

That is the problem, people think that we are getting 16 bit resolution of material that is 40-60dB down from the operating level. The bits are not there.

Very true especially for recordings of classical music with low average sound level. 24bits or DSD are much better.

 

[PMA]

Quantization distortion is very, very well known. That's why we use dither and the anti-imaging filter.

Yes, but we only get "smoother" sound. Resolution remains the same or is LOWERED.

 

[SY]

PMA: That does not turn out to be the case. Please read the extensive sets of papers by Lipshitz on this subject:

J. Vanderkooy and S.P. Lipshitz. 1987. Dither in digital audio. J. Audio Eng. Soc. 35, 966-975.

J. Vanderkooy and S.P. Lipshitz. 1989. Digital dither: Signal processing with resolution far below the least significant bit. Proc. AES 7th International Conference "Audio in Digital Times", Toronto, Canada, May 14-17, 1989.

S.P. Lipshitz, J. Vanderkooy and R.A. Wannamaker. 1991. Minimally audible noise shaping. J. Audio Eng. Soc. 39, 836-852.

S.P. Lipshitz, R.A. Wannamaker and J. Vanderkooy. 1992. Quantization and dither: A theoretical survey. J. Audio Eng. Soc. 40, 355-375.

 

[PMA]

SY, thank you very much. I know the papers on dither, and different dithering methods as well. No dither would give you more than 16bits resolution from 16bits quantization. What you get is randomizing of quantization error, and change in SFDR. We are not here to repeat such basics.

 

[Joachim Gerhard]

When i record my little band, i use double speed DSD. When i downconvert to 16/44 and listen to the CD i burned, i can interstingly hear the biggest diffences in the bass. It sounds less warm and musical. Well, we do not have a drummer, it´s more guitar, bass and vocals and some beats from the drum computer so my material is not particular rich in treble transients.

 

[SY]

Then you're using a nonstandard definition of "resolution," especially in the context of your response to myrrh. Please give me yours.

 

[PMA]

Okay, I should have said "no new information". Interleaved computed samples do not bring new information. But interleaved samples are a product of oversampling, not the dither. Dither in fact masks last +/-0.5LSB or +/-1LSB.

 

[SY]

Please define "masks" in the context you're using it. Does the -60dB noise of a phono stage "mask" information? The -70-80dB of tape noise?

BTW, here's a nice layman's explanation of the relationship between dither and resolution:

Daqarta - Dither: Noise + Averaging = Resolution

 

[SY]

Stereophile: Bryston BDA-1 D/A converter

I'd call your attention to Figure 3 and Figure 6.

 

[scott wurcer]

Okay, I should have said "no new information". Interleaved computed samples do not bring new information. But interleaved samples are a product of oversampling, not the dither. Dither in fact masks last +/-0.5LSB or +/-1LSB.

In a properly band limited system there is no new information to get. The interpolated samples are exact within aperature and amplitude error. Your use of "mask" is unclear here.

 

[PMA]

Please define "masks" in the context you're using it. Does the -60dB noise of a phono stage "mask" information? The -70-80dB of tape noise?

Tape or vinyl is not the case now. We are speaking about dither and resolution. For 16 bits, 1LSB = 1/65536 of Full Scale Range. This is a Resolution of 16 bit quantization. No dithering method is able to increase it.