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2022-10-11 09:19:14 UTC
Flicker 1/f Bass Noise and Pace
Op Amp noise can rise sharply in the bass frequencies below 1KHz. Taking a noise (µVrms) reading at 100Hz or at 50Hz, from the plot of noise by frequency, gives an indication of likely flicker 1/f noise.
The NE5532 IC op amp, used in the CD550c, has noise of 1.1Vrms at 100Hz (Figure 1 page 6 datasheet). That is an increase in noise, at 100Hz, of about 50% over its average figure of 0.7 Vrms and noise continues to rise as frequency falls. Bass instruments, with the NE5532/CD550c, could not be made out so well and were a bit lost in large ensemble pieces. There was, however, no noticeable problems with bass, with this op amp and player, playing solo instruments or small ensemble pieces and bass sounded clear and musical. The Exposure 2010S2 uses two https://highfidelity.pl/@main-97&lang=en NE5532s and https://www.whathifi.com/exposure/2010s2/review What Hi Fi? said of this player that the bass suffers from thinness and a lack of resolution. 1/f noise?
It needs to be said that you probably won't notice 1/f noise, if your system does not go much below 100Hz or if your system has a highier noise floor than the op amps or if you only listen to rhymically straight forward or single instrument bass.
Flicker 1/f Noise and Pace
What flicker noise means is that noise is not linear over the audio frequency range. And the bass, due to the 1/f noise, is heard, with some material, differently to the rest of the frequency band. This audio difference is thought to be interpreted as pace errors, but only with complex material.
Recently I have been experimenting with the 1/f compromised OPA1602 and this op amp had pace problems for about 5% of CDs played, even though it has a highish slew (20V/μs) value. For the OPA1602 noise increased from 0.27µVrms at 1kHz to 0.32 at 100Hz (18% increase) and to about 0.41µVrms (52% increase) at 50Hz (Figure 1 page 5 datasheet). However there is some doubt as to the gain compatibility of the OPA1602 in the host CD player (CD753) and this will have a performance impact. And there may well be other compatibility factors.
Julia Wolfe’s fast paced, complex and congested piece Lick (Bang on a Can) https://www.gramophone.co.uk/review/bang-on-a-can-industry is accurately presented using the high slew OP275 (22V/μs) in a CD753 but seems a bit muddled and had a perceived pace issue with the NE5532 (9V/μs) in a CA CD550c. The increase in 1/f bass noise of the NE5532 op amp below 100Hz, and the hypothesised effect of 1/f on noise linearity over frequency and on perceived pace, may have implications here. The OP275, in comparison, has no rise in 1/f noise. The NE5532/CD550c (9V/μs) excelled in playing rhythmically and bass simple but pacey opera.
Further, pace issues were identified in a shunt resistor based pre amplifiers, see https://www.tnt-audio.com/amplpreamp_shunt_comparison_e.html, and it is, perhaps, telling that resistors also have 1/f noise. The link between 1/f noise and percieved pace is, though, a hypothesis and needs further research and observation. Any thoughts?
Op Amp noise can rise sharply in the bass frequencies below 1KHz. Taking a noise (µVrms) reading at 100Hz or at 50Hz, from the plot of noise by frequency, gives an indication of likely flicker 1/f noise.
The NE5532 IC op amp, used in the CD550c, has noise of 1.1Vrms at 100Hz (Figure 1 page 6 datasheet). That is an increase in noise, at 100Hz, of about 50% over its average figure of 0.7 Vrms and noise continues to rise as frequency falls. Bass instruments, with the NE5532/CD550c, could not be made out so well and were a bit lost in large ensemble pieces. There was, however, no noticeable problems with bass, with this op amp and player, playing solo instruments or small ensemble pieces and bass sounded clear and musical. The Exposure 2010S2 uses two https://highfidelity.pl/@main-97&lang=en NE5532s and https://www.whathifi.com/exposure/2010s2/review What Hi Fi? said of this player that the bass suffers from thinness and a lack of resolution. 1/f noise?
It needs to be said that you probably won't notice 1/f noise, if your system does not go much below 100Hz or if your system has a highier noise floor than the op amps or if you only listen to rhymically straight forward or single instrument bass.
Flicker 1/f Noise and Pace
What flicker noise means is that noise is not linear over the audio frequency range. And the bass, due to the 1/f noise, is heard, with some material, differently to the rest of the frequency band. This audio difference is thought to be interpreted as pace errors, but only with complex material.
Recently I have been experimenting with the 1/f compromised OPA1602 and this op amp had pace problems for about 5% of CDs played, even though it has a highish slew (20V/μs) value. For the OPA1602 noise increased from 0.27µVrms at 1kHz to 0.32 at 100Hz (18% increase) and to about 0.41µVrms (52% increase) at 50Hz (Figure 1 page 5 datasheet). However there is some doubt as to the gain compatibility of the OPA1602 in the host CD player (CD753) and this will have a performance impact. And there may well be other compatibility factors.
Julia Wolfe’s fast paced, complex and congested piece Lick (Bang on a Can) https://www.gramophone.co.uk/review/bang-on-a-can-industry is accurately presented using the high slew OP275 (22V/μs) in a CD753 but seems a bit muddled and had a perceived pace issue with the NE5532 (9V/μs) in a CA CD550c. The increase in 1/f bass noise of the NE5532 op amp below 100Hz, and the hypothesised effect of 1/f on noise linearity over frequency and on perceived pace, may have implications here. The OP275, in comparison, has no rise in 1/f noise. The NE5532/CD550c (9V/μs) excelled in playing rhythmically and bass simple but pacey opera.
Further, pace issues were identified in a shunt resistor based pre amplifiers, see https://www.tnt-audio.com/amplpreamp_shunt_comparison_e.html, and it is, perhaps, telling that resistors also have 1/f noise. The link between 1/f noise and percieved pace is, though, a hypothesis and needs further research and observation. Any thoughts?