The following conversation occurred during the cross-examination of Dr Stipp.
Roux: What we do know is that she was in the toilet – and the toilet windows were closed – on the State’s version. Stipp: That’s correct Roux: And the accused was outside the toilet where we say to you the window was open. Stipp: That’s correct. Roux: I can understand he screams, but what I will put to you in the Defence’s case – when someone is in that toilet it is a closed confined space with a closed window and a closed door you would not hear a woman screaming and in any event not so distinct that you will make out emotion ... if she was inside the toilet. (Record 374, lines 14–19)
Here we have the defence putting it to Dr Stipp that it was impossible for him to hear Reeva scream from the toilet, or that in any case he would not have been able to hear the screams so distinct that he would have been able to make out the emotion of the screams.
We put it to Advocate Roux that he didn’t know what he was talking about – even his own acoustic expert Ivan Lin contradicted him later during the trial.
What did the defence’s expert, Ivan Lin, say?
At plus minus 80 metres away, if the sound emanated from the toilet, sub-point: if the listener was on the balcony a scream emanating from the toilet at source, can range from 46 dBA to 48 dBA. Based on the ambient noise levels there at the listener’s location of between 20 dBA and 45 dBA. The sound is in the range of audible and intelligible. (Record 2654, lines 2–7)
Let’s first look at the lay of the land.
The Stipps’ house is 72 meters away from the side of Oscar’s house where the bathroom and toilet windows are situated. (Not 80 metres as incorrectly assumed by the defence’s acoustic expert). There were no buildings in between. There was a direct line of sight from inside the Stipps’ bedroom, as well as from the two balconies.
When the Stipps heard the “first sounds” they were inside their bedroom with both balcony doors open to some degree. Moments after the “first sounds” they moved to these balconies to listen to the screaming emanating from Oscar’s house.
The small rectangle to the right in the photo below is the window to the toilet in which Reeva was killed.
Sometime around 3 am Mrs Stipp woke up – she was feeling a bit ill. She stayed in bed as she pondered on whether to get up for a drink of water or not. When she finally decided to get up for a drink of water she heard three sounds that sounded to her like gunshots. These sounds also woke up her husband, Dr Stipp.
“Moments” after hearing the “first sounds” both Mrs and Dr Stipp moved to the balconies. While standing on the balconies they listened to the screams. They weren’t sure where the screams came from. They saw that the light in Oscar’s bathroom was on. Dr Stipp saw someone with a fair complexion walk in the bathroom from right to left. Mrs Stipp testified that she is absolutely convinced it was a woman’s screams she heard – judging by the pitch and tonal character of the scream. Shortly before the “second sounds” she also heard a man’s voice occurring at the same time as the screams. She even remarked to her husband that she was hearing a man’s voice.
The defence retained Ivan Lin, an acoustic expert, to answer the following question: Could the State witnesses hear the screams well enough to differentiate between a male and female scream?
To start his analysis Lin made an assumption that Reeva would have screamed at a sound level of 110 dBA. At How Loud Can a Woman Scream? we discuss in detail why we think this was an unrealistic assumption, chosen to support Oscar’s version and not to assist the court, as one would expect from an expert witness. Based on research a sound level of 120 dBA would have been a much more realistic and honest value. However, we will show that even with an assumption of 110 dBA the Reeva’s screams would still have been both audible and intelligible to the Stipps to the extent that they would have been able to tell the difference between a male and female scream.
The defence expert assumed that the closed bathroom window would have reduced the sound level of the scream by 25 dBA at a distance of 1 metre away from the window. He also assumed that a scream in the bathroom would be attenuated by about 9 dBA through the open bathroom window.
- Sound Level in bathroom = 110 dBA (120 dBA)
- Sound Level at 1 meter outside bathroom window = 85 dBA (95 dBA)
Using an acoustical formula one can calculate by how much the sound level would dissipate over a given distance. In his analysis Ivan Lin used a distance of 80 metres, while the actual distance is 72 metres. Another error in favour of his client. Over a distance of 80 m the SPL would decrease by about 38 dBA.
- SPL on Stipp balconies = 47 dBA (58 dBA)
Whether these SPL’s would have been audible and intelligible depends on the level of ambient (background) noise at the time. The difference between the sound level of a noise (e.g. scream) and the ambient noise level is called the signal to noise ratio (SNR).
For sound to be intelligible we need an SNR of at least 6 dB. Intelligibility then increases as the sound become more audible. Ideally one need a SNR of 10-15 dB for good intelligibility.
Therefore another critical assumption that requires careful consideration is the level of ambient noise. The question is what would the ambient noise level have been in the Stipp bedroom at 3 am in the morning, in a sparsely developed residential estate – far removed from major sources of ambient noise such as busy highways or commercial and industrial zones?
The defence expert assumed a range of 20 dBA to 45 dBA (apparently based on his own personal experience). This range is so wide that it is pretty much useless. The upper limit of 45 dBA is unrealistically high. Please read our research into Ambient Noise as to why we think an ambient noise level of 30–35 dBA would have been a far more realistic and honest assumption.
Why didn’t the defence rather measure the ambient noise level in the estate itself at 3 am in the morning? They didn’t because the results would have been detrimental to their case.
Based on a conservative ambient noise level of 35 dBA the SNR to someone on the balconies would have been about 12 dB (23 dB).
Larger than 6 dB makes it audible, and between 10 and 15 dB makes it very intelligible.
- Screams from the toilet through a closed window would have been both audible and intelligible to Dr and Mrs Stipp where they stood on their balconies, irrespective of whether Reeva screamed at 110 dBA or 120 dBA.
- Similarly, screams from the bathroom through an open window would also have been audible and intelligible to Dr and Mrs Stipp where they stood on their balconies.
- The level of intelligibility would have been high enough for the Stipps to also discern the emotion in the screams – irrespective of whether Oscar or Reeva screamed, and irrespective of whether the screams were at 110 dBA or 120 dBA
- The defence wasn’t honest when they argued – “when someone is in that toilet it is a closed confined space with a closed window and a closed door you would not hear a woman screaming and in any event not so distinct that you will make out emotion … if she was inside the toilet.”
Read more in our book Oscar vs. The Truth.